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Hard Drive Technologies
"It would appear that we have
reached the limits of what it is
possible to achieve with
computer technology, although
one should be careful with such
statements, as they tend to
sound pretty silly in five years."
In this chapter, you will learn
f all the hardware on a PC, none gets more attention--or gives more
how to
anguish--than the hard drive. There's a good reason for this: if the hard
Explain how hard drives work
drive breaks, you lose data. As you probably know, when the data goes, you
Identify and explain the ATA
have to redo work or restore from backup--or worse. It's good to worry about
hard drive interfaces
the data, because the data runs the office, maintains the payrolls, and stores the
Identify and explain the SCSI
hard drive interfaces
e-mail. This level of concern is so strong that even the most neophyte PC users
Describe how to protect data
are exposed to terms such as IDE, ATA, and controller--even if they don't put
with RAID
the terms into practice!
Explain how to install drives
This chapter focuses on how hard drives work, beginning with the internal
Configure CMOS and install
layout and organization of the hard drive. You'll look at the different types of
Troubleshoot hard drive
hard drives used today (PATA, SATA, and SCSI), how they interface with the
PC, and how to install them properly into a system. The chapter covers how
more than one drive may work with other drives to provide data safety and
improve speed through a feature called RAID. Let's get started.
How Hard Drives Work
All hard drives are composed of individual disks, or platters, with read/
write heads on actuator arms controlled by a servo motor--all contained in
a sealed case that prevents contamination by outside air (see Figure 8.1).
The aluminum platters are
coated with a magnetic medium.
Cross Check
Two tiny read/write heads ser-
vice each platter, one to read the
Implementing Hard Drives
top and the other to read the bot-
In the Essentials book you covered the process of implementing a
tom of the platter (see Figure 8.2).
preinstalled drive. What are the two steps that must be performed on ev-
The coating on the platters is
ery installed hard drive so that the operating system can use the drive?
phenomenally smooth! It has to
be, as the read/write heads actu-
ally float on a cushion of air above
the platters, which spin at speeds between 3500 and 10,000
rpm. The distance (flying height) between the heads and the
disk surface is less than the thickness of a fingerprint. The
closer the read/write heads are to the platter, the more
densely the data packs onto the drive. These infinitesimal
tolerances demand that the platters never be exposed to out-
side air. Even a tiny dust particle on a platter would act like
a mountain in the way of the read/write heads and would
cause catastrophic damage to the drive. To keep the air clean
inside the drive, all hard drives use a tiny, heavily filtered
aperture to keep the air pressure equalized between the
interior and the exterior of the drive.
Data Encoding
Although the hard drive stores data in binary form, visual-
izing a magnetized spot representing a one and a non-mag-
netized spot representing a zero grossly oversimplifies
the process. Hard drives store data in tiny magnetic
Figure 8.1
Inside the hard drive
Figure 8.2
Top and bottom read/write heads and armatures
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
fields--think of them as tiny magnets
that can be placed in either direction on
the platter, as shown in Figure 8.3. Each
tiny magnetic field, called a flux, can  ∑ Figure 8.3  Data is stored in tiny magnetic fields.
switch back and forth through a process
called a flux reversal (see Figure 8.4).
Electronic equipment can read and
write flux reversals much faster and
easier than it can magnetize or not mag-
netize a spot to store a one or a zero.
In early hard drives, as the read/
write head moved over a spot, the direc-
tion of the flux reversal defined a one or
a zero. As the read/write head passed
from the left to the right, it recognized  ∑ Figure 8.4  Flux reversals
fluxes in one direction as a zero and the
other direction as a one (Figure 8.5).
Hard drives read these flux reversals at
a very high speed when accessing or
writing data.
Today's hard drives use a more
complex  and  efficient  method  to
Figure 8.5  Fluxes are read in one direction as 0 and the other direction as 1.
interpret flux reversals using special
data encoding systems. Instead of
reading individual fluxes, a modern
hard drive reads groups of fluxes called
runs. Starting around 1991, hard drives
began using a data encoding system
known as run length limited (RLL). With
RLL, any combination of ones and
zeroes can be stored in a preset
combination of about 15 different runs.
The hard drive looks for these runs and
reads them as a group, resulting in
much faster and much more dense data.
Whenever you see RLL, you also see
two numbers: the minimum and the
Figure 8.6  Sequential RLL runs
maximum run length, such as RLL 1,7
or RLL 2,7. Figure 8.6 shows two
sequential RLL runs.
Current drives use an extremely advanced method of RLL called Par-
tial Response Maximum Likelihood (PRML) encoding. As hard drives pack
more and more fluxes on the drive, the individual fluxes start to interact
with each other, making it more and more difficult for the drive to verify
where one flux stops and another starts. PRML uses powerful, intelligent
circuitry to analyze each flux reversal and to make a "best guess" as to what
type of flux reversal it just read. As a result, the maximum run length for
PRML drives reaches up to around 16 to 20 fluxes, far more than the 7 or so
on RLL drives. Longer run lengths enable the hard drive to use more com-
plicated run combinations so that the hard drive can store a phenomenal
Chapter 8: Hard Drive Technologies
amount of data. For example, a run of only 12 fluxes on a hard drive might
equal a string of 30 or 40 ones and zeroes when handed to the system from
the hard drive.
The size required by each magnetic flux on a hard drive has reduced
considerably over the years, resulting in higher capacities. As fluxes become
smaller, they begin to interfere with each other in weird ways. I have to say
weird since to make sense of what's going on at this subatomic level (I told
you these fluxes were small!) would require that you take a semester of
quantum mechanics! Let's just say that laying fluxes flat against the platter
has reached its limit. To get around this problem, hard drive makers re-
cently began to make hard drives that store their flux reversals vertically (up
and down) rather than longitudinally (forward and backward), enabling
them to make hard drives in the 1 terabyte (1024 gigabyte) range. Manufac-
turers call this vertical storage method perpendicular recording (Figure 8.7).
For all this discussion and detail on data encoding, the day-to-day PC
technician never deals with encoding. Sometimes, however, knowing what
you don't need to know helps as much as knowing what you do need to
know. Fortunately, data encoding is inherent to the hard drive and com-
pletely invisible to the system. You're never going to have to deal with data
encoding, but you'll sure sound smart when talking to other PC techs if you
know your RLL from your PRML!
Moving the Arms
The read/write heads move across the platter on the ends of actuator arms. In
the entire history of hard drives, manufacturers have used only two technol-
ogies to move the arms: stepper motor and voice coil . Hard drives first used
stepper motor technology, but today they've all moved to voice coil.
Stepper motor technology moved the arm in fixed increments or steps,
but the technology had several limitations that doomed it. Because the inter-
face between motor and actuator arm required minimal slippage to ensure
precise and reproducible movements, the positioning of the arms became
less precise over time. This physical deterioration caused data transfer er-
Floppy disk drives still use
rors. Additionally, heat deformation wreaked havoc with stepper motor
stepper motors.
drives. Just as valve clearances in automobile engines change with operat-
ing temperature, the positioning accuracy changed as the PC operated and
various hard drive components got warmer. Although very small, these
changes caused problems. Accessing the data written on a cold hard drive,
for example, became difficult after the disk warmed. In addition, the read/
write heads could damage the disk surface if not "parked" (set in a non-data
area) when not in use, requiring techs to use special parking programs
before transporting a step-
per motor drive.
All hard drives made
today employ a linear motor
to move the actuator arms.
The  linear  motor,  more
popularly called a voice coil
motor, uses a permanent
magnet surrounding a coil on
Figure 8.7  Perpendicular versus traditional longitudinal recording
the actuator arm. When an
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
electrical current passes, the coil generates a magnetic field that moves the
Tech Tip
actuator arm. The direction of the actuator arm's movement depends on the
polarity of the electrical current through the coil. Because the voice coil and the
Fluid Bearings
actuator arm never touch, no degradation in positional accuracy takes place
Currently, almost all hard drives
over time. Voice coil drives automatically park the heads when the drive loses
use a motor located in the center
power, making the old stepper motor park programs obsolete.
spindle supporting the drive plat-
ters. Traditionally, tiny ball bear-
Lacking the discrete "steps" of the stepper motor drive, a voice coil drive
ings support the spindle motor,
cannot accurately predict the movement of the heads across the disk. To
and as disk technology has ad-
make sure voice coil drives land exactly in the correct area, the drive re-
vanced, these ball bearings have
serves one side of one platter for navigational purposes. This area essen-
become the limiting factor in the
tially "maps" the exact location of the data on the drive. The voice coil
three critical design criteria for
moves the read/write head to its best guess about the correct position on the
hard drives: rotational speed,
hard drive. The read/write head then uses this map to fine-tune its true po-
storage capacity, and noise levels.
sition and make any necessary adjustments.
The higher the rotational speed of
Now that you have a basic understanding of how a drive physically
a drive, the more the metal-on-
stores data, let's turn to how the hard drive organizes that data so we can
metal contact creates heat and lu-
use that drive.
bricant problems that impact the
lifespan of the bearings. However
precisely machined, ball bearings
are not perfectly round. The mea-
surement of how much they wob-
Have you ever seen a cassette tape? If you look at the actual brown Mylar (a
ble (and thus how much the drive
type of plastic) tape, nothing will tell you whether sound is recorded on that
platters wobble), called runout, is
tape. Assuming the tape is not blank, however, you know something is on the
now the limiting factor on how
tape. Cassettes store music in distinct magnetized lines. You could say that
densely you can pack information
the physical placement of those lines of magnetism is the tape's "geometry."
together on a disk drive.
Geometry also determines where a hard drive stores data. As with a cas-
The technological fix for this
sette tape, if you opened up a hard drive, you would not see the geometry.
comes in the form of fluid bear-
But rest assured that the drive has geometry; in fact, every model of hard
ings. A fluid bearing is basically
a small amount of lubricant
drive uses a different geometry. We describe the geometry for a particular
trapped in a carefully machined
hard drive with a set of numbers representing three values: heads, cylin-
housing. The use of fluid in place
ders, and sectors per track.
of metal balls means that no con-
tact occurs between metal sur-
faces to generate heat and wear.
The number of heads for a specific hard drive describes, rather logically, the
The fluid also creates no mechani-
number of read/write heads used by the drive to store data. Every platter
cal vibration, so fluid bearings
can support higher rotational
requires two heads. If a hard drive has four platters, for example, it would
speeds. The runout of a fluid
need eight heads (see Figure 8.8).
bearing is about one-tenth that of
Based on this description of heads, you would think that hard drives
the best ball bearing, significantly
would always have an even number of heads, right? Wrong! Most hard
increasing potential information
drives reserve a head or two for their own use. Therefore, a hard drive can
density. The absence of a mechan-
have either an even or an odd number of heads.
ical connection between moving
parts also dramatically reduces
noise levels, and the fluid itself
acts to dampen the sound further.
To visualize cylinders, imagine taking a soup can and opening both ends of
Finally, liquid bearings provide
the can. Wash off the label and clean out the inside. Now look at the shape of
better shock resistance than ball
the can; it is a geometric shape called a cylinder. Now imagine taking that
cylinder and sharpening one end so that it easily cuts through the hardest
metal. Visualize placing the ex-soup can over the hard drive and pushing it
down through the drive. The can cuts into one side and out the other of
Chapter 8: Hard Drive Technologies
Figure 8.8
Two heads per platter
each platter. Each circle transcribed by the can is where you store data on the
drive, and is called a track (Figure 8.9).
Each side of each platter contains tens of thousands of tracks. Interest-
ingly enough, the individual tracks themselves are not directly part of the
drive geometry. Our interest lies only in the groups of tracks of the same di-
ameter, going all of the way through the drive. Each group of tracks of the
same diameter is called a cylinder (see Figure 8.10).
There's more than one cylinder! Go get yourself about a thousand more
cans, each one a different diameter, and push them through the hard drive.
A typical hard drive contains thousands of cylinders.
Sectors per Track
Now imagine cutting the hard drive like a birthday cake, slicing all the
tracks into tens of thousands of small slivers. Each sliver is called a sector,
and each sector stores 512 bytes of data (see Figure 8.11). Note that sector
Figure 8.9
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
refers to the sliver when discussing geometry, but it refers to the
specific spot on a single track within that sliver when discussing
data capacity.
The sector is the universal "atom" of all hard drives. You
can't divide data into anything smaller than a sector. Although
sectors are important, the number of sectors is not a geometry.
The geometry value is called sectors per track (sectors/track).
The sectors/track value describes the number of sectors in each
track (see Figure 8.12).
The Big Three
Cylinders, heads, and sectors/track combine to define the hard
drive's geometry. In most cases, these three critical values are
referred to as CHS. The importance of these three values lies in
the fact that the PC's BIOS needs to know the drive's geometry
to know how to talk to the drive. Back in the old days, a techni-
cian needed to enter these values into the CMOS setup program
manually. Today, every hard drive stores the CHS information
in the drive itself, in an electronic format that enables the BIOS
to query the drive automatically to determine these values.
You'll see more on this later in the chapter in the section called
Two other values--write precompensation cylinder and  ∑ Figure 8.10
landing zone--no longer have relevance in today's PCs; how-
ever, these terms still are tossed around and a few CMOS setup
utilities still support them--another classic example of a technology appen-
dix! Let's look at these two holdouts from another era so when you access
CMOS, you won't say, "What the heck are these?"
Write Precompensation Cylinder
Older hard drives had a real problem with the fact that sectors toward the
inside of the drives were much smaller than sectors toward the outside. To
handle this, an older drive would spread data a little farther apart once it got
to a particular cylinder. This cylinder was called the write precompensation
Figure 8.11
Chapter 8: Hard Drive Technologies
(write precomp) cylinder, and the PC had to know
which cylinder began this wider data spacing. Hard
drives no longer have this problem, making the write
precomp setting obsolete.
Landing Zone
On older hard drives with stepper motors, the landing
zone value designated an unused cylinder as a "parking
Figure 8.12
place" for the read/write heads. As mentioned earlier,
Sectors per track
old stepper motor hard drives needed to have their
read/write heads parked before being moved in order to
avoid accidental damage. Today's voice coil drives park
themselves whenever they're not accessing data, automatically placing the
read/write heads on the landing zone. As a result, the BIOS no longer needs
the landing zone geometry.
IT Technician
Tech Tip
ATA--The King
The term IDE (integrated drive
electronics) refers to any hard
Over the years, many interfaces existed for hard drives, with such names as
drive with a built-in controller.
ST-506 and ESDI. Don't worry about what these abbreviations stood for;
All hard drives are technically
neither the CompTIA A+ certification exams nor the computer world at
IDE drives, although we only use
large has an interest in these prehistoric interfaces. Starting around 1990, an
the term IDE when discussing
interface called ATA appeared that now virtually monopolizes the hard
ATA drives.
drive market. ATA hard drives are often referred to as integrated drive elec-
tronics (IDE) drives. Only one other type of interface, the moderately popu-
lar small computer system interface (SCSI), has any relevance for hard
Tech Tip
drives. ATA drives come in two basic flavors. The older parallel ATA
(PATA) drives send data in parallel, on a 40- or 80-wire data cable. PATA
External Hard Drives
drives dominated the industry for more than a decade but are being re-
A quick trip to any major com-
placed by serial ATA (SATA) drives that send data in serial, using only one
puter store will reveal a thriving
wire for data transfers. The leap from PATA to SATA is only one of a large
trade in external hard drives. You
used to be able to find external
number of changes that have taken place over the years with ATA. To appre-
drives that connected to the slow
ciate these changes, we'll run through the many ATA standards forwarded
parallel port, but external drives
over the years.
today connect to a FireWire,
Hi-Speed USB 2.0, or eSATA
port. All three interfaces offer
high data transfer rates and
When IBM unveiled the 80286-powered IBM PC AT in the early 1980s, it in-
hot-swap capability, making them
troduced the first PC to include BIOS support for hard drives. This BIOS
ideal for transporting huge files
supported up to two physical drives, and each drive could be up to 504 MB--
such as digital video clips. Re-
far larger than the 5-MB and 10-MB drives of the time. Although having
gardless of the external interface,
however, inside the casing you'll
built-in support for hard drives certainly improved the power of the PC, at
find an ordinary PATA or SATA
that time, installing, configuring, and troubleshooting hard drives could at
drive, just like those described in
best be called difficult.
this chapter.
To address these problems, Western Digital and Compaq developed a
new hard drive interface and placed this specification before the American
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
National Standards Institute (ANSI) committees, which in turn put out the AT
Attachment (ATA) interface in March of 1989. The ATA interface specified a
The ANSI subcommittee di-
cable and a built-in controller on the drive itself. Most importantly, the ATA
rectly responsible for the ATA
standard is called Technical
standard used the existing AT BIOS on a PC, which meant that you didn't
Committee T13. If you want to
have to replace the old system BIOS to make the drive work--a very impor-
know what's happening with
tant consideration for compatibility but one that would later haunt ATA
ATA, check out the T13 Web site:
drives. The official name for the standard, ATA, never made it into the com-
mon vernacular until recently, and then only as PATA to distinguish it from
SATA drives.
Early ATA Physical Connections
The first ATA drives connected to the computer with a 40-pin ribbon cable
that plugged into the drive and to a hard drive controller. The cable has a
colored stripe down one side that denotes pin 1 and should connect to the
drive's pin 1 and to the controller's pin 1. Figure 8.13 shows the "business
end" of an early ATA drive, with the connectors for the ribbon cable and the
power cable.
The controller is the support circuitry that acts as the intermediary be-
tween the hard drive and the external data bus. Electronically, the setup
looks like Figure 8.14.
Wait a minute! If ATA drives
are IDE (see the Tech Tip), they al-
ready have a built-in controller.
Why do they then have to plug into
a controller on the motherboard?
Well, this is a great example of a
term that's not used properly, but
everyone (including the mother-
board and hard drive makers) uses
it this way. What we call the ATA
controller is really no more than an
interface providing a connection to
the rest of the PC system. When
your BIOS talks to the hard drive, it  ∑ Figure 8.13  Back of IDE drive showing 40-pin connector (left), jumpers (center), and
actually talks to the onboard cir-
power connector (right)
cuitry on the drive, not the connec-
tion on the motherboard. But, even
though the real controller resides on the hard drive, the
40-pin connection on the motherboard is called the con-
troller. We have a lot of misnomers to live with in the
ATA world!
The ATA-1 standard defined that no more than two
drives attach to a single IDE connector on a single ribbon
cable. Because up to two drives can attach to one connec-
tor via a single cable, you need to be able to identify each
drive on the cable. The ATA standard identifies the two
different drives as "master" and "slave." You set one
drive as master and one as slave using tiny jumpers on  ∑ Figure 8.14  Relation of drive, controller, and bus
the drives (Figure 8.15).
Chapter 8: Hard Drive Technologies
Figure 8.15
A typical hard drive with directions for setting a jumper
The controllers are on the motherboard and manifest themselves as two
40-pin male ports, as shown in Figure 8.16.
PIO and DMA Modes
If you're making a hard drive standard, you must define both the method
and the speed at which the data's going to move. ATA-1 defined two differ-
ent methods, the first using programmed I/O (PIO) addressing and the sec-
ond using direct memory access (DMA) mode.
Figure 8.16
IDE interfaces on a motherboard
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
PIO is nothing more than the traditional I/O addressing scheme, where
the CPU talks directly to the hard drive via the BIOS to send and receive
data. Three different PIO speeds called PIO modes were initially adopted:
PIO mode 0: 3.3 MBps (megabytes per second)
PIO mode 1: 5.2 MBps
PIO mode 2: 8.3 MBps
DMA modes defined a method to enable the hard drives to talk to RAM
directly using old-style DMA commands. (The ATA folks called this single
word DMA.) This old-style DMA was slow, and the resulting three ATA sin-
gle word DMA modes were also slow:
Single word DMA mode 0: 2.1 MBps
Single word DMA mode 1: 4.2 MBps
Single word DMA mode 2: 8.3 MBps
When a computer booted up, the BIOS queried the hard drive to see
what modes it could use and would then automatically adjust to the fastest
In 1990, the industry adopted a series of improvements to the ATA standard
called ATA-2. Many people called these new features Enhanced IDE (EIDE) .
The terms ATA, IDE, and EIDE
EIDE was really no more than a marketing term invented by Western Digi-
are used interchangeably.
tal, but it caught on in common vernacular and is still used today, although
its use is fading. Regular IDE drives quickly disappeared, and by 1995, EIDE
drives dominated the PC world. Figure 8.17 shows a typical EIDE drive.
Figure 8.17
EIDE drive
Chapter 8: Hard Drive Technologies
ATA-2 was the most important ATA standard, as it included powerful
new features such as higher capacities; support for non­hard drive storage
devices; support for two more ATA devices, for a maximum of four; and
substantially improved throughput.
Higher Capacity with LBA
IBM created the AT BIOS to support hard drives many years before IDE
Hard drive makers talk about
drives were invented, and every system had that BIOS. The developers of
hard drive capacities in millions
IDE made certain that the new drives would run from the same AT BIOS
and billions of bytes, not mega-
command set. With this capability, you could use the same CMOS and BIOS
bytes and gigabytes!
routines to talk to a much more advanced drive. Your motherboard or hard
drive controller wouldn't become instantly obsolete when you installed a
new hard drive.
Unfortunately, the BIOS routines for the original AT command set allowed
a hard drive size of only up to 528 million bytes (or 504 MB--remember that a
mega = 1,048,576, not 1,000,000). A drive could have no more than 1024 cyl-
inders, 16 heads, and 63 sectors/track:
1024 cylinders ◊ 16 heads ◊ 63 sectors/track ◊ 512 bytes/sector = 504 MB
For years, this was not a problem. But when hard drives began to ap-
proach the 504 MB barrier, it became clear that there needed to be a way of
getting past 504 MB. The ATA-2 standard defined a way to get past this limit
with logical block addressing (LBA) . With LBA, the hard drive lies to the
computer about its geometry through an advanced type of sector transla-
tion. Let's take a moment to understand sector transla-
tion, and then come back to LBA.
Sector Translation  Long before hard drives approached
the 504 MB limit, the limits of 1024 cylinders, 16 heads,
and 63 sectors/track gave hard drive makers fits. The
big problem was the heads. Remember that every two
heads means another platter, another physical disk that
you have to squeeze into a hard drive. If you wanted a
hard drive with the maximum number of 16 heads, you
would need a hard drive with eight physical platters
inside the drive! Nobody wanted that many platters: it
made the drives too tall, it took more power to spin up
the drive, and that many parts cost too much money (see
Figure 8.18).
Figure 8.18
Too many heads
Manufacturers could readily produce a hard drive
that had fewer heads and more cylinders, but the stupid
1024/16/63 limit got in the way. Plus, the traditional
sector arrangement wasted a lot of useful space. Sectors
toward the inside of the drive, for example, are much
shorter than the sectors on the outside. The sectors on the
outside don't need to be that long, but with the tradi-
tional geometry setup, hard drive makers had no choice.
They could make a hard drive store a lot more informa-
tion, however, if hard drives could be made with more
Figure 8.19
Multiple sectors/track
sectors/track on the outside tracks (see Figure 8.19).
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
The ATA specification was designed to have two geometries. The physi-
cal geometry defined the real layout of the CHS inside the drive. The logical
geometry described what the drive told the CMOS. In other words, the IDE
drive "lied" to the CMOS, thus side-stepping the artificial limits of the BIOS.
When data was being transferred to and from the drive, the onboard cir-
cuitry of the drive translated the logical geometry into the physical geome-
try. This function was, and still is, called sector translation .
Let's look at a couple of hypothetical examples in action. First, pretend
that Seagate came out with a new,
cheap, fast hard drive called the
ST108. To get the ST108 drive fast
Table 8.1
Seagate's ST108 Drive Geometry
and cheap, however, Seagate had
ST108 Physical
BIOS Limits
to use a rather strange geometry,
shown in Table 8.1.
Notice that the cylinder num-
ber is greater than 1024. To over-
come this problem, the IDE drive
performs a sector translation that
Total Capacity
108 MB
reports a geometry to the BIOS that
is totally different from the true ge-
ometry of the drive. Table 8.2
Table 8.2
Physical and Logical Geometry of the ST108 Drive
shows the actual geometry and the
"logical" geometry of our mythical
ST108 drive. Notice that the logical
geometry is now within the accept-
able parameters of the BIOS limita-
tions. Sector translation never
changes the capacity of the drive; it
changes only the geometry to stay
Total Capacity
108 MB
Total Capacity
108 MB
within the BIOS limits.
Back to LBA  Now let's watch how the advanced sector translation of LBA
provides support for hard drives greater than 504 MB. Let's use an old drive,
the Western Digital WD2160, a 2.1-GB hard drive, as an example. This drive is
no longer in production but its smaller CHS values make understanding LBA
easier. Table 8.3 lists its physical and logical geometries.
Note that, even with sector translation, the number of heads is greater than
the allowed 16! So here's where the magic of LBA comes in. The WD2160 is ca-
pable of LBA. Now assuming that the BIOS is also capable of LBA, here's
what happens. When the com-
puter boots up, the BIOS asks the
Table 8.3
Western Digital WD2160's Physical
drives if they can perform LBA. If
and Logical Geometries
they say yes, the BIOS and the
drive work together to change the
way they talk to each other. They
can do this without conflicting
with the original AT BIOS com-
mands by taking advantage of un-
used commands to use up to 256
Total Capacity
2.1 GB
Total Capacity
2.1 GB
heads. LBA enables support for a
Chapter 8: Hard Drive Technologies
maximum of 1024 ◊ 256 ◊ 63 ◊ 512 bytes = 8.4-GB hard drives. Back in 1990, 8.4
GB was hundreds of time larger than the drives used at the time. Don't worry,
later ATA standards will get the BIOS up to today's huge drives!
Not Just Hard Drives Anymore: ATAPI
ATA-2 added an extension to the ATA specification, called Advanced Tech-
With the introduction of
ATAPI, the ATA standards are
nology Attachment Packet Interface (ATAPI) , that enabled non­hard drive
often referred to as ATA/ATAPI
devices such as CD-ROM drives and tape backups to connect to the PC via
instead of just ATA.
the ATA controllers. ATAPI drives have the same 40-pin interface and mas-
ter/slave jumpers as ATA hard drives. Figure 8.20 shows an ATAPI
CD-RW drive attached to a motherboard. The key
difference between hard drives and every other
type of drive that attaches to the ATA controller is
in how the drives get BIOS support. Hard drives
get it through the system BIOS, whereas non­hard
drives require the operating system to load a
software driver.
More Drives with ATA-2
ATA-2 added support for a second controller,
raising the total number of supported drives from
two to four. Each of the two controllers is equal in
power and capability. Figure 8.21 is a close-up of
a typical motherboard, showing the primary con-
troller marked as IDE1 and the secondary marked
as IDE2.
Increased Speed
Figure 8.20
ATAPI CD-RW drive attached to a motherboard via a
standard, 40-pin ribbon cable
ATA-2 defined two new PIO modes and a new
type of DMA called multi-word DMA that was a
substantial improvement over the old DMA.
Figure 8.21
Primary and secondary controllers labeled on a motherboard
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Technically, multi-word DMA was still the old-style DMA, but it worked in
a much more efficient manner so it was much faster.
PIO mode 3: 11.1 MBps
PIO mode 4: 16.6 MBps
Multi-word DMA mode 0: 4.2 MBps
Multi-word DMA mode 1: 13.3 MBps
Multi-word DMA mode 2: 16.6 MBps
ATA-3 came on quickly after ATA-2 and added
one new feature called Self-Monitoring, Analy-
sis, and Reporting Technology (S.M.A.R.T. , one
of the few PC acronyms that requires the use of
periods after each letter). S.M.A.R.T. helps pre-
dict when a hard drive is going to fail by moni-
toring the hard drive's mechanical components.
S.M.A.R.T. is a great idea and is popular in
specialized server systems, but it's complex, im-
perfect, and hard to understand. As a result, only
a few utilities can read the S.M.A.R.T. data on
your hard drive. Your best sources are the hard
drive manufacturers. Every hard drive maker
has a free diagnostic tool (that usually works
only for their drives) that will do a S.M.A.R.T.
check along with other tests. Figure 8.22 shows
Western Digital's Data Lifeguard Tool in action.
Note that it says only whether the drive has
passed or not. Figure 8.23 shows some S.M.A.R.T.
Figure 8.22
Data Lifeguard
Figure 8.23
S.M.A.R.T. information
Chapter 8: Hard Drive Technologies
Although you can see the actual S.M.A.R.T. data, it's generally useless or
indecipherable. It's best to trust the manufacturer's opinion and run the
software provided.
Anyone who has opened a big database file on a hard drive appreciates that
a faster hard drive is better. ATA-4 introduced a new DMA mode called
Ultra DMA that is now the primary way a hard drive communicates with a
PC. Ultra DMA uses DMA bus mastering to achieve far faster speeds than
was possible with PIO or old-style DMA. ATA-4 defined three Ultra DMA
Ultra DMA mode 0: 16.7 MBps
Ultra DMA mode 2, the most
popular of the ATA-4 DMA
Ultra DMA mode 1: 25.0 MBps
modes, is also called ATA/33.
Ultra DMA mode 2: 33.3 MBps
INT13 Extensions
Here's an interesting factoid for you: The original ATA-1 standard allowed
for hard drives up to 137 GB! It wasn't the ATA standard that caused the
504-MB size limit, it was the fact that the standard used the old AT BIOS and
the BIOS, not the ATA standard, could support only 504 MB. LBA was a
work-around that told the hard drive to lie to the BIOS to get it up to 8.4 GB.
But eventually hard drives started edging close to the LBA limit and some-
thing had to be done. The T13 folks said, "This isn't our problem! It's the an-
cient BIOS problem. You BIOS makers need to fix the BIOS!" And they did.
In 1994, Phoenix Technologies (the BIOS manufacturer) came up with a
new set of BIOS commands called Interrupt 13 (INT13) extensions . INT13
extensions broke the 8.4-GB barrier by completely ignoring the CHS values
and instead feeding the LBA a stream of addressable sectors. A system with
INT13 extensions can handle drives up to 137 GB. The entire PC industry
quickly adopted INT13 extensions and every system made since 2000­2001
supports INT13 extensions.
Ultra DMA was such a huge hit that the ATA folks adopted two faster Ultra
DMA modes with ATA-5:
Ultra DMA mode 4, the most
popular of the ATA-5 DMA
Ultra DMA mode 3: 44.4 MBps
modes, is also called ATA/66.
Ultra DMA mode 4: 66.6 MBps
Ultra DMA modes 4 and 5 ran so quickly that the ATA-5 standard de-
fined a new type of ribbon cable of handling the higher speeds. This 80-wire
cable still has 40 pins on the connectors, but it includes another 40 wires
in the cable that act as grounds to improve the cable's ability to handle
high-speed signals. The 80-wire cable, just like the 40-pin ribbon cable, has a
colored stripe down one side give you proper orientation for pin 1 on the
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
controller and the hard drive. Previous ver-
sions of ATA didn't define where the differ-
ent drives were plugged into the ribbon
cable, but ATA-5 defined exactly where the
controller, master, and slave drives con-
nected, even defining colors to identify
them. Take a look at the ATA/66 cable in
Figure 8.24. The connector on the left is col-
ored blue (which you could see if the photo
was in color!)--that connector must be the
one used to plug into the controller. The
connector in the middle is grey--that's for
the slave drive. The connector on the right is  ∑ Figure 8.24  ATA/66 cable
black--that's for the master drive. Any
ATA/66 controller connections are colored
blue to let you know it is an ATA/66
ATA/66 is backward compatible, so you may safely plug an earlier
drive into an ATA/66 cable and controller. If you plug an ATA/66 drive
into an older controller it will workjust not in ATA/66 mode. The only
risky action is to use an ATA/66 controller and hard drive with a non-ATA/
66 cable. Doing so will almost certainly cause nasty data losses!
Hard drive size exploded in the early 21st century and the seemingly
impossible-to-fill 137-GB limit created by INT13 extensions became a bar-
rier to fine computing more quickly than most people had anticipated.
When drives started hitting the 120-GB mark, the T13 committee adopted an
industry proposal pushed by Maxtor (a major hard drive maker) called Big
Drive that increased the limit to more than 144 petabytes (approximately
144,000,000 GB). T13 also thankfully gave the new standard a less-silly
name, calling it ATA/ATAPI-6 or simply ATA-6 . Big Drive was basically just
a 48-bit LBA, supplanting the older 24-bit addressing of LBA and INT13 ex-
tensions. Plus, the standard defined an enhanced block mode, enabling
drives to transfer up to 65,536 sectors in one chunk, up from the measly 256
sectors of lesser drive technologies.
ATA-6 also introduced Ultra DMA mode 5, kicking the data transfer rate
up to 100 MBps. Ultra DMA mode 5 is more commonly referred to as ATA/
100, which requires the same 80-wire connectors as ATA/66.
ATA-7 brought two new innovations to the ATA worldone evolutionary
and the other revolutionary. The evolutionary innovation came with the last
of the parallel ATA Ultra DMA modes; the revolutionary was a new form of
ATA called serial ATA (SATA).
Chapter 8: Hard Drive Technologies
ATA-7 introduced the fastest and probably least adopted of all the ATA
speeds, Ultra DMA mode 6 ( ATA/133 ). Even though it runs at a speed of
133 MBps, the fact that it came out with SATA kept many hard drive manu-
facturers away. ATA/133 uses the same cables as Ultra DMA 66 and 100.
While you won't find many ATA/133 hard drives, you will find plenty
of ATA/133 controllers. There's a trend in the industry to color the control-
ler connections on the hard drive red, although this is not part of the ATA-7
Serial ATA
The real story of ATA-7 is SATA. For all its longevity as the mass storage in-
terface of choice for the PC, parallel ATA has problems. First, the flat ribbon
cables impede airflow and can be a pain to insert properly. Second, the ca-
bles have a limited length, only 18 inches. Third, you can't hot-swap PATA
drives. You have to shut down completely before installing or replacing a
drive. Finally, the technology has simply reached the limits of what it can do
in terms of throughput.
Serial ATA addresses these issues. SATA creates a point-to-point connec-
tion between the SATA device--hard disk, CD-ROM, CD-RW, DVD-ROM,
DVD-RW, and so on--and the SATA controller. At a glance, SATA devices
look identical to standard PATA devices. Take a closer look at the cable and
power connectors, however, and you'll see significant differences (Figure 8.25).
Because SATA devices send data serially instead of in parallel, the
SATA interface needs far fewer physical wires--seven instead of the eighty
wires that is typical of PATA--resulting in much thinner cabling. This
might not seem significant, but the benefit is that thinner cabling means
better cable control and better airflow through the PC case, resulting in
better cooling.
Data port
Power port
Data cable
Power cable
Figure 8.25
SATA hard drive cables and connectors
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Further, the maximum SATA device cable length is more than twice that
Tech Tip
of an IDE cable--about 40 inches (1 meter) instead of 18 inches. Again, this
might not seem like a big deal, unless you've struggled to connect a PATA
SATA Names
hard disk installed into the top bay of a full-tower case to an IDE connector
Number-savvy readers might
located all the way at the bottom of the motherboard!
have noticed a discrepancy be-
SATA does away with the entire master/slave concept. Each drive con-
tween the names and throughput
of the two SATA drives. After all,
nects to one port, so no more daisy-chaining drives. Further, there's no maxi-
mum number of drivesmany motherboards are now available that support
1.5 Gb per second throughput
translates to 192 MB per second,
up to eight SATA drives. Want more? Snap in a SATA host card and load
a lot higher than the advertised
'em up!
speed of a "mere" 150 MBps. The
The big news, however, is in data throughput. As the name implies,
same is true of the 3Gb/300 MBps
SATA devices transfer data in serial bursts instead of parallel, as PATA de-
drives. The encoding scheme used
vices do. Typically, you might not think of serial devices as being faster than
on SATA drives takes about
parallel, but in this case, that's exactly the case. A SATA device's single
20 percent of the overhead for the
stream of data moves much faster than the multiple streams of data coming
drive, leaving 80 percent for pure
from a parallel IDE device--theoretically up to 30 times faster! SATA drives
bandwidth. The 3Gb drive created
come in two common varieties, the 1.5Gb and the 3Gb, that have a maxi-
all kinds of problems, because the
mum throughput of 150 MBps and 300 MBps, respectively.
name of the committee working
on the specifications was called
SATA is backward compatible with current PATA standards and en-
the SATA II committee, and mar-
ables you to install a parallel ATA device, including a hard drive, optical
keters picked up on the SATA II
drive, and other devices, to a serial ATA controller by using a SATA bridge .
name. As a result, you'll find
A SATA bridge manifests as a tiny card that you plug directly into the
many brands called SATA II
40-pin connector on a PATA drive. As you can see in Figure 8.26, the con-
rather than 3Gb. The SATA com-
troller chip on the bridge requires separate power; you plug a Molex con-
mittee now goes by the name
nector into the PATA drive as normal. When you boot the system, the PATA
drive shows up to the system as a SATA drive.
SATA's ease of use has made it the choice for desktop system storage,
and its success is already showing in the fact that more than 90 percent of all
hard drives sold today are SATA drives.
Figure 8.26
SATA bridge
Chapter 8: Hard Drive Technologies
External SATA (eSATA) extends
the SATA bus to external devices,
as the name would imply. The
eSATA drives use similar connec-
tors to internal SATA, but they're
keyed differently so you can't mis-
take one for the other. Figure 8.27
shows eSATA connectors on the
back of a motherboard. eSATA uses
shielded cable lengths up to 2 me-
ters outside the PC and is hot
pluggable. The beauty of eSATA is
that it extends the SATA bus at full
speed, so you're not limited to the
meager 50 or 60 MBps of FireWire
or USB.
Figure 8.27
eSATA connectors (center; that's a FireWire port on the left)
SCSI: Still Around
Many specialized server machines and enthusiasts' systems use the small
computer system interface (SCSI) technologies for various pieces of core
hardware and peripherals, from hard drives to printers to high-end tape
The CompTIA A+ 220-604
backup machines. SCSI is different from ATA in that SCSI devices connect
exam tests you on SCSI and
together in a string of devices called a chain. Each device in the chain gets a
RAID, topics essential to server
SCSI ID to distinguish it from other devices on the chain. Last, the ends of a
SCSI chain must be terminated. Let's dive into SCSI now, and see how SCSI
chains, SCSI IDs, and termination all work.
SCSI is an old technology dating from the late 1970s, but it has been con-
tinually updated. SCSI is faster than ATA
(though the gap is closing fast), and until
SATA arrived SCSI was the only good
choice for anyone using RAID (see the
"RAID" section a little later). SCSI is ar-
guably fading away, but it still deserves
some mention.
SCSI Chains
SCSI manifests itself through a  SCSI
chain , a series of SCSI devices working
together through a host adapter. The host
adapter provides the interface between
the SCSI chain and the PC. Figure 8.28
shows a typical PCI host adapter. Many
techs refer to the host adapter as the SCSI
controller, so you should be comfortable
Figure 8.28
with both terms.
SCSI host adapter
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
All SCSI devices can be divided
into two groups: internal and external.
Internal SCSI devices are attached in-
side the PC and connect to the host
adapter through the latter's internal
connector. Figure 8.29 shows an inter-
nal SCSI device, in this case a CD-ROM
drive. External devices hook to the ex-
ternal connector of the host adapter.
Figure 8.30 is an example of an external
SCSI device.
Internal SCSI devices connect to
the host adapter with a 68-pin ribbon
cable (Figure 8.31). This flat, flexible ca-
ble functions precisely like a PATA
cable. Many external devices connect to
the host adapter with a 50-pin high
density (HD) connector. Figure 8.32
shows a host adapter external port.
Higher end SCSI devices use a 68-pin
high density (HD) connector.
Figure 8.29  Internal SCSI CD-ROM
Multiple internal devices can be
connected together simply by using a
cable with enough connectors. Figure 8.33, for example, shows a cable that
can take up to four SCSI devices, including the host adapter.
Assuming the SCSI host adapter has a standard external port (some con-
trollers don't have external connections at all), plugging in an external SCSI
device is as simple as running a cable from device to controller. The external
SCSI connectors are D-shaped, so you can't plug them in backward. As an
added bonus, some external SCSI devices have two ports, one to connect to
the host adapter and a second to connect to another SCSI device. The process
of connecting a device directly to another device is called daisy-chaining.
Figure 8.30
Figure 8.31
Back of external SCSI device
Typical 68-pin ribbon cable
Chapter 8: Hard Drive Technologies
You can daisy-chain up to 15 devices to one host adapter. SCSI
chains can be internal, external, or both (see Figure 8.34).
If you're going to connect a number of devices on the same
SCSI chain, you must provide some way for the host adapter to
tell one device from another. To differentiate devices, SCSI
uses a unique identifier called the SCSI ID . The SCSI ID num-
ber can range from 0 to 15. SCSI IDs are similar to many other
Figure 8.32  50-pin HD port on SCSI host adapter
PC hardware settings in that a SCSI device can theoretically
have any SCSI ID, as long as that ID is not already taken by an-
other device connected to the same host adapter.
Some conventions should be followed when setting SCSI IDs. Typically,
Old SCSI equipment allowed
most people set the host adapter to 7 or 15, but you can change this setting.
SCSI IDs from 0 to 7 only.
Note that there is no order for the use of SCSI IDs. It does not matter which
device gets which number, and you
can skip numbers. Restrictions on
IDs apply only within a single chain.
Two devices can have the same ID, in
other words, as long as they are on
different chains (Figure 8.35).
Every SCSI device has some
method of setting its SCSI ID. The
trick is to figure out how as you're
holding the device in your hand. A
SCSI device may use jumpers, dip
switches, or even tiny dials; every
new SCSI device is a new adventure
as you try to determine how to set its
Figure 8.33
Internal SCSI chain with two devices
Figure 8.34
Internal and external devices on one SCSI chain
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Whenever you send a signal down a wire, some of
that signal reflects back up the wire, creating an
echo and causing electronic chaos. SCSI chains use
termination to prevent this problem. Termination
simply means putting something on the ends of the
wire to prevent this echo. Terminators are usually
pull-down resistors and can manifest themselves in
many different ways. Most of the devices within a
PC have the appropriate termination built in. On
other devices, including SCSI chains and some net-
work cables, you have to set termination during
The rule with SCSI is that you must terminate  ∑ Figure 8.35  IDs don't conflict between separate SCSI chains.
only the ends of the SCSI chain. You have to termi-
nate the ends of the cable, which usually means that
you need to terminate the two devices at the ends of the cable. Do not termi-
nate devices that are not on the ends of the cable. Figure 8.36 shows some ex-
amples of where to terminate SCSI devices.
Because any SCSI device might be on the end of a chain, most manufac-
turers build SCSI devices that can self-terminate. Some devices will detect
that they are on the end of the SCSI chain and will automatically terminate
themselves. Most devices, however, require that you set a jumper or switch to
enable termination (Figure 8.37).
Figure 8.36
Figure 8.37
Location of the terminated devices
Setting termination
Chapter 8: Hard Drive Technologies
Protecting Data with RAID
Ask experienced techs, "What is the most expensive part of a PC?" and
they'll all answer in the same way: "It's the data." You can replace any sin-
gle part of your PC for a few hundred dollars at most, but if you lose critical
data--well, let's just say I know of two small companies that went out of
business just because they lost a hard drive full of data.
Data is king; data is your PC's raison d'Ítre. Losing data is a bad thing, so
you need some method to prevent data loss. Now, of course, you can do
backups, but if a hard drive dies, you have to shut down the computer, rein-
stall a new hard drive, reinstall the operating system, and then restore the
backup. There's nothing wrong with this as long as you can afford the time
and cost of shutting down the system.
A better solution, though, would save your data if a hard drive died and
enable you to continue working throughout the process. This is possible if
you stop relying on a single hard drive and instead use two or more drives
to store your data. Sounds good, but how do you do this? Well, first of all,
you could install some fancy hard drive controller that reads and writes
data to two hard drives simultaneously (Figure 8.38). The data on each drive
would always be identical. One drive would be the primary drive and the
other drive, called the mirror drive, would not be used unless the primary
drive failed. This process of reading and writing data at the same time to
two drives is called disk mirroring .
If you really want to make data safe, you can use two separate control-
lers for each drive. With two drives, each on a separate controller, the
system will continue to operate,
even if the primary drive's control-
ler stops working. This super-drive
mirroring technique is called disk
duplexing (Figure 8.39). Disk du-
plexing is also much faster than
disk mirroring because one control-
ler does not write each piece of data
Even though duplexing is faster
than mirroring, they both are
slower than the classic one drive,
one controller setup. You can use
multiple drives to increase your
hard drive access speed. Disk strip-
ing (without parity) means spread-
ing the data among multiple (at
least two) drives. Disk striping by
itself provides no redundancy. If
you save a small Microsoft Word
file, for example, the file is split into
multiple pieces; half of the pieces go
on one drive and half on the other
(Figure 8.40).
Figure 8.38
Mirrored drives
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Figure 8.39
Duplexing drives
Figure 8.40
Disk striping
Chapter 8: Hard Drive Technologies
The one and only advantage of disk striping is speed--it is a fast way to
read and write to hard drives. But if either drive fails, all data is lost. Disk
striping is not something you should do--unless you're willing to increase
the risk of losing data to increase the speed at which your hard drives save
and restore data.
Disk striping with parity , in contrast, protects data by adding extra infor-
mation, called parity data, that can be used to rebuild data should one of the
drives fail. Disk striping with parity requires at least three drives, but it is
common to use more than three. Disk striping with parity combines the best
of disk mirroring and plain disk striping. It protects data and is quite fast.
The majority of network servers use a type of disk striping with parity.
A couple of sharp guys in Berkeley back in the 1980s organized the many
An array in the context of
techniques for using multiple drives for data protection and increasing
RAID refers to a collection of two
speeds as the redundant array of independent (or inexpensive) disks (RAID) .
or more hard drives.
They outlined seven levels of RAID, numbered 0 through 6.
RAID 0--Disk Striping  Disk striping requires at least two drives.
It does not provide redundancy to data. If any one drive fails, all
data is lost.
RAID 1--Disk Mirroring/Duplexing  RAID 1 arrays require at
least two hard drives, although they also work with any even
number of drives. RAID 1 is the ultimate in safety, but you lose
storage space since the data is duplicated--you need two 100-GB
drives to store 100 GB of data.
RAID 2--Disk Striping with Multiple Parity Drives  RAID 2 was
a weird RAID idea that never saw practical use. Unused, ignore it.
RAID 3 and 4--Disk Striping with Dedicated Parity  RAID 3 and
4 combined dedicated data drives with dedicated parity drives. The
differences between the two are trivial. Unlike RAID 2, these
versions did see some use in the real world but were quickly
replaced by RAID 5.
RAID 5--Disk Striping with Distributed Parity  Instead of
dedicated data and parity drives, RAID 5 distributes data and parity
information evenly across all drives. This is the fastest way to
Tech Tip
provide data redundancy. RAID 5 is by far the most common RAID
implementation and requires at least three drives. RAID 5 arrays
RAID Lingo
effectively use one drive's worth of space for parity. If, for example,
No tech worth her salt says
you have three 200-GB drives, your total storage capacity is 400 GB.
things like, "We're implementing
If you have four 200-GB drives, your total capacity is 600 GB.
disk striping with parity." Use
the RAID level. Say, "We're im-
RAID 6--Disk Striping with Extra Parity  If you lose a hard drive
plementing RAID 5." It's more
in a RAID 5 array, your data is at great risk until you replace the bad
accurate and very impressive to
hard drive and rebuild the array. RAID 6 is RAID 5 with extra parity
the folks in the accounting
information. RAID 6 needs at least five drives, but in exchange you
can lose up to two drives at the same time. RAID 6 is gaining in
popularity for those willing to use larger arrays.
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
After these first RAID levels were defined, some manufacturers came up
with ways to combine different RAIDs. For example, what if you took two
You'll hear the term nested
pairs of striped drives and mirrored the pairs? You would get what is called
RAID used for multiple RAID
solutions. The terms are
RAID 0+1. Or what (read this carefully now) if you took two pairs of mir-
rored drives and striped the pairs? You then get what we call RAID 1+0 or
what is often called RAID 10. Combinations of different types of single
RAID are called multiple RAID solutions. Multiple RAID solutions, while
enjoying some support in the real world, are quite rare when compared to
There is actually a term for a
single RAID solutions RAID 0, 1, and 5.
storage system composed of
multiple independent disks,
rather than disks organized us-
Implementing RAID
ing RAID: JBOD, which stands
for Just a Bunch of Disks (or
RAID levels describe different methods of providing data redundancy or
enhancing the speed of data throughput to and from groups of hard drives.
They do not say how to implement these methods. Literally thousands of dif-
ferent methods can be used to set up RAID. The method used depends
largely on the desired level of RAID, the operating system used, and the
thickness of your wallet.
The obvious starting place for RAID is to connect at least two hard
drives in some fashion to create a RAID array. For many years, if you
wanted to do RAID beyond RAID 0 and RAID 1, the only technology you
could use was good-old SCSI. SCSI's chaining of multiple devices to a single
controller made it a natural for RAID. SCSI drives make superb RAID ar-
rays, but the high cost of SCSI drives and RAID-capable host adapters kept
RAID away from all but the most critical systems--usually big file servers.
In the last few years, substantial leaps in ATA technology have made
ATA a viable alternative to SCSI drive technology for RAID arrays. Special-
ized ATA RAID controller cards support ATA RAID arrays of up to 15
drives--plenty to support even the most complex RAID needs. In addition,
the inherent hot-swap capabilities of serial ATA have virtually guaranteed
that serial ATA will quickly take over the lower end of the RAID business.
Try This!
Managing Heat with Multiple Drives
Adding three or more fast hard drives into a cramped PC case can be a
recipe for disaster to the unwary tech. All those disks spinning con-
stantly create a phenomenal amount of heat. Heat kills PCs! You've got
to manage the heat inside a RAID-enabled system or risk losing your
data, drives, and basic system stability. The easiest way to do this is to
add fans, so Try This!
Open up your PC case and look for built-in places to mount fans.
How many case fans do you have installed now? What size are they?
What sizes can you use? (Most cases use 80 mm fans, but 60 and 120 mm
fans are common as well.) Jot down the particulars of your system and
take a trip to the local PC store to check out the fans.
Before you get all fan-happy and grab the biggest and baddest fans
to throw in your case, don't forget to think about the added noise level.
Try to get a compromise between keeping your case cool enough and
not causing early deafness!
Chapter 8: Hard Drive Technologies
Personally, I think the price and performance of serial ATA mean SCSI's
days are numbered.
Once you have a number of hard drives, the next question is whether to
use hardware or software to control the array. Let's look at both options.
Hardware versus Software
You can use Disk Manage-
ment in Windows 2000 and Win-
All RAID implementations break down into either hardware or software meth-
dows XP Professional to create
ods. Software is often used when price takes priority over performance. Hard-
RAID 1 and RAID 5 arrays, but
ware is used when you need speed along with data redundancy. Software
you can use Disk Management
only remotely on a server ver-
RAID does not require special controllers--you can use the regular ATA con-
sion of Windows (2000 Server or
trollers or SCSI host adapters to make a software RAID array. But you do need
Server 2003). In other words, the
"smart" software. The most common software implementation of RAID is the
capability is there, but Microsoft
built-in RAID software that comes with Windows 2000 Server and Windows
has limited the OS. If you want
Server 2003. The Disk Management program in these Windows Server ver-
to use software RAID in Win-
dows 2000 or XP (Home or Pro-
sions can configure drives for RAID 0, 1, or 5, and it works with ATA or SCSI
fessional), you need to use a
(Figure 8.41). Disk Management in Windows 2000 Professional and Windows
third-party tool to set it up.
XP Professional, in contrast, can only do RAID 0.
Windows Disk Management is not the only software RAID game in
town. A number of third-party software programs can be used with Win-
dows or other operating systems.
Software RAID means the operating system is in charge of all RAID
functions. It works for small RAID solutions but tends to overwork your op-
erating system easily, creating slowdowns. When you really need to keep
going, when you need RAID that doesn't even let the users know a problem
has occurred, hardware RAID is the answer.
Hardware RAID centers around an intelligent controller--either a SCSI
host adapter or an ATA controller that handles all of the RAID functions
(Figure 8.42). Unlike a regular ATA controller or SCSI host adapter, these
controllers have chips that know how to "talk RAID."
Figure 8.41
Disk Management in Windows Server 2003
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Figure 8.42
Serial ATA RAID controller
Most RAID setups in the real world are hardware-based. Almost all of
the many hardware RAID solutions provide hot-swapping--the ability to re-
place a bad drive without disturbing the operating system. Hot-swapping is
common in hardware RAID.
Hardware-based RAID is invisible to the operating system and is config-
ured in several ways, depending on the specific chips involved. Most RAID
systems have a special configuration utility in Flash ROM that you access af-
ter CMOS but before the OS loads. Figure 8.43 shows a typical firmware pro-
gram used to configure a hardware RAID solution.
Personal RAID
Due to drastic reductions in the cost of ATA RAID controller chips, in
the last few years we've seen an explosion of ATA-based hardware RAID
Figure 8.43
RAID configuration utility
Chapter 8: Hard Drive Technologies
solutions built into mainstream motherboards. While this "ATA RAID on
the motherboard" began with parallel ATA, the introduction of serial ATA
RAID controllers aren't just
made motherboards with built-in RAID extremely common.
for internal drives; some models
can handle multiple eSATA
These personal RAID motherboards might be quite common, but
drives configured using any of
they're not used too terribly often given that these RAID solutions usually
the different RAID levels. If
provide only RAID 0 or RAID 1. If you want to use RAID, spend a few extra
you're feeling lucky, you can cre-
dollars and buy a RAID 5­capable controller.
ate a RAID array using both in-
ternal and external SATA drives.
The Future Is RAID
RAID has been with us for about 20 years, but until only recently it was the
domain of big systems and deep pockets. During those 20 years, however, a
number of factors have come together to make RAID a reality for both big
servers and common desktop systems. Imagine a world where dirt-cheap
RAID on every computer means no one ever again losing critical data. I get
goose bumps just thinking about it!
Connecting Drives
Installing a drive is a fairly simple process if you take the time to make sure
you've got the right drive for your system, configure the drive properly,
and do a few quick tests to see if it's running properly. Since PATA, SATA,
and SCSI have different cabling requirements, we'll look at each of these
Choosing Your Drive
First, decide where you're going to put the drive. Look for an open ATA
connection. Is it PATA or SATA? Is it a dedicated RAID controller? Many
motherboards with built-in RAID controllers have a CMOS setting that en-
ables you to turn the RAID on or off (Figure 8.44). Do you have the right con-
troller for a SCSI drive?
Figure 8.44
Settings for RAID in CMOS
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Second, make sure you have room for the drive in the case. Where will
you place it? Do you have a spare power connector? Will the data and power
cables reach the drive? A quick test fit is always a good idea.
Don't worry about PIO Modes and DMAa new drive will support
anything your controller wants to do.
Jumpers and Cabling
on PATA Drives
If you have only one hard drive, set the drive's
jumpers to master or standalone. If you have two
drives, set one to master and the other to slave. See
Figure 8.45 for a close-up of a PATA hard drive
showing the jumpers.
At first glance, you might notice that the jump-
ers aren't actually labeled master and slave. So how
do you know how to set them properly? The easi-
est way is to read the front of the drive; most
drives have a diagram on the housing that explains
how to set the jumpers properly. Figure 8.46 shows
the front of one of these drives, so you can see how
to set the drive to master or slave.
Hard drives may have other jumpers that may
or may not concern you during installation. One  ∑ Figure 8.45  Master/slave jumpers on a hard drive
common set of jumpers is used for diagnostics at
the manufacturing plant or for special settings in
other kinds of devices that use hard drives. Ignore
them. They have no bearing in the PC world. Second, many drives provide a
third setting, which is used if only one drive connects to a controller. Often,
Most of the high speed ATA/
66/100/133 cables support cable
master and single drive are the same setting on the hard drive, although
select--try one and see!
some hard drives require separate settings. Note that the name for the single
drive setting varies among manufacturers. Some use Single; others use 1
Drive or Standalone.
Many current PATA hard drives use a jumper setting called cable select,
rather than master or slave. As the name implies, the position on the cable
determines which drive will be master or slave: master on the end, slave in
the middle. For cable select to work properly with two drives, both
drives must be set as cable select and the cable itself must be a spe-
cial cable-select cable. If you see a ribbon cable with a pinhole
through one wire, watch out! That's a cable-select cable.
If you don't see a label on the drive that tells you how to set the
jumpers, you have several options. First, look for the drive maker's
Web site. Every drive manufacturer lists its drive jumper settings on
the Web, although it can take a while to find the information you
want. Second, try phoning the hard drive maker directly. Unlike
many other PC parts manufacturers, hard drive producers tend to
stay in business for a long period of time and offer great technical
Hard drive cables have a colored stripe that corresponds to the  ∑ Figure 8.46  Drive label showing master/slave
number-one pin--called pin 1--on the connector. You need to make
Chapter 8: Hard Drive Technologies
certain that pin 1 on the controller
Cross Check
is on the same wire as pin 1 on the
hard drive. Failing to plug in the
Molex Connectors
drive properly will also prevent
Hard drives and other internal devices use Molex connectors for power.
the PC from recognizing the drive.
Check your memory from the Essentials course. What voltages go
If you incorrectly set the master/
through the four wires on a Molex connector? What should you note
slave jumpers or cable to the hard
about the connector and inserting it into the corresponding socket on
drives, you won't break anything;
the drive?
it just won't work.
Finally, you need to plug a
Molex connector from the power supply into the drive. All modern PATA
drives use a Molex connector.
Cabling SATA Drives
Installing SATA hard drives is even easier than installing IDE devices due to
the fact that there's no master, slave, or cable select configuration to mess
with. In fact, there are no jumper settings to worry about at
all, as SATA supports only a single device per controller
channel. Simply connect the power and plug in the control-
ler cable as shown in Figure 8.47--the OS automatically de-
tects the drive and it's ready to go! The keying on SATA
controller and power cables makes it impossible to install
either incorrectly.
The biggest problem with SATA drives is that many
motherboards come with four or more. Sure, the cabling is
easy enough, but what do you do when it comes time to
start the computer and the system is trying to find the right
hard drive to boot up! That's where CMOS comes into
Connecting SCSI Drives
Figure 8.47
Properly connected SATA cable
Connecting SCSI drives requires three things. You must
use a controller that works with your drive. You need to set
unique SCSI IDs on the controller and the drive. Finally,
you need to connect the ribbon cable and power connections properly. With
SCSI, you need to attach the data cable correctly. You can reverse a PATA
cable, for example, and nothing happens except the drive doesn't work. If
you reverse a SCSI cable, however, you can seriously damage the drive. Just
as with PATA cables, pin 1 on the SCSI data cable must go to pin 1 on both
the drive and the host adapter.
BIOS Support: Configuring CMOS
and Installing Drivers
Every device in your PC needs BIOS support, and the hard drive controllers
are no exception. Motherboards provide support for the ATA hard drive
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
controllers via the system BIOS, but they require configuration in CMOS for
the specific hard drives attached. SCSI drives require software drivers or
firmware on the host adapter.
In the old days, you had to fire up CMOS and manually enter CHS infor-
mation whenever you installed a new ATA drive to ensure the system saw
the drive. Today, this process still takes place, but it's much more auto-
mated. Still, there's plenty to do in CMOS when you install a new hard
CMOS settings for hard drives vary a lot among motherboards. The fol-
lowing information provides a generic look at the most common settings,
but you'll need to look at your specific motherboard manual to understand
all the options available.
Configuring Controllers
As a first step in configuring controllers, make certain they're enabled. It's
easy to turn off controllers in CMOS, and many motherboards turn off sec-
ondary ATA controllers by default. Scan through your CMOS settings to lo-
cate the controller on/off options (see Figure 8.48 for typical settings). This
is also the time to check whether your onboard RAID controllers work in
both RAID and non-RAID settings.
If the controllers are enabled and the drive is properly connected, the drive
should appear in CMOS through a process called autodetection. Autodetection
is a powerful and handy feature, but it seems every CMOS has a different
way to manifest it, and how it is manifested may affect how your computer
decides which hard drive to try to boot when you start your PC.
One of your hard drives stores the operating system needed when you
boot your computer, and your system needs a way to know where to look
for this operating system. The traditional BIOS supported a maximum of
only four ATA drives on two controllers, called the primary controller and the
secondary  controller.  The  BIOS
looked for the master drive on the
primary controller when the system
booted up. If you used only one
controller, you used the primary
controller. The secondary controller
was used for CD-ROMs, DVDs, or
other non-bootable drives.
Older CMOS made this clear
and easy, as shown in Figure 8.49.
When you booted up, the CMOS
would query the drives through
autodetection, and whatever drives
the CMOS saw would show up
here. Some even older CMOS had a
Autodetect that you had to run to  ∑ Figure 8.48  Typical controller settings in CMOS
Chapter 8: Hard Drive Technologies
see the drives in this screen. There
are places for up to four de-
vicesnotice not all of them actu-
ally have a device.
The autodetection screen indi-
cated that you installed a PATA
drive correctly. If you installed a
hard drive on the primary controller
as master, but messed up the jumper
and set it to slave, it would show up
in the autodetection screen as the
slave. If you had two drives and set
them both to master, one drive or the
other (or sometimes both) didn't ap-
pear, telling you that something was
messed up in the physical installa-
Figure 8.49
Old standard CMOS settings
tion. If you forgot to plug in the rib-
bon cable or the power, the drives
wouldn't autodetect.
SATA messed up the autodetection happiness. There's no such thing as
master, slave, or even primary and secondary controller in the SATA world.
To get around this, motherboards with PATA and SATA today use a num-
bering systemand every motherboard uses its own numbering system!
One common numbering method uses the term channels for each controller.
The first boot device is channel 1, the second is channel 2, and so on. PATA
channels may have a master and a slave, but a SATA channel has only a
master, as SATA controllers support only one drive. So instead of names of
drives, you see numbers. Take a look at Figure 8.50.
Whew! Lots of hard drives! This motherboard supports the traditional
four PATA drives, but it also supports four SATA drives. Each controller is
assigned a numbernote that channel 1 and channel 2 have master/slave
settings, and that's how you know channel 1 and 2 are the PATA drives.
Channels 3 through 6 are SATA, even though the listing says master.
(SATA's still somewhat new, and a
CMOS using incorrect terms like
master is common.)
Boot Order
If you want your computer to run,
it's going to need an operating sys-
tem to boot. While the PCs of our
forefathers (those of the 1980s and
early 1990s) absolutely required
you to put the operating system on
the primary master, most BIOS
makers by 1995 enabled you to put
the OS on any of the four drives and
then tell the system through CMOS
which hard drive to boot. Addition-
Figure 8.50
New standard CMOS features
ally, you may need to boot from
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
a floppy, CD-ROM, or even a thumb drive at times. CMOS takes
care of this by enabling you to set a boot order.
Figure 8.51 shows a typical boot order screen. It has a first, sec-
ond, and third boot option. Many users like to boot first from floppy
or CD-ROM, and then from a hard drive. This enables them to put in
Figure 8.51  Boot order
a bootable floppy or CD-ROM if they're having problems with the
system. Of course, you can set it to boot first from your hard drive
and then go into CMOS and change it when you need toit's your
Most modern CMOS lump the
Try This!
hard drive boot order onto a sec-
ond screen. This screen works like
Working with CMOS
an autodetect in that it shows only
One of the best ways to get your mind around the different drive stan-
actual hard drives attached. This
dards and capabilities is to run benchmarking software on the hard
beats the heck out of guessing!
drive to get a baseline of its capabilities. Then, change CMOS settings to
alter the performance of the drive and run the diagnostics again. Try
Device Drivers
Devices that do not get BIOS via the
Get a reliable hard drive benchmarking program. I recommend
system BIOS routines naturally re-
HD Tach (www.simplisoftware.com) as reliable and rugged.
quire some other source for BIOS.
Run the software, and record the scores.
For ATAPI devices and many
Change some or all of the following CMOS settings, and then
SATA controllers, the source of
run the benchmarking utility again: PIO mode, DMA mode,
choice is software device drivers,
Block mode.
but both technologies have a couple
What were the effects of changing settings?
of quirks you should know about.
ATAPI Devices and BIOS
ATAPI drives plug into an ATA controller on the motherboard and follow
the same conventions on cabling and jumpers used by PATA hard drives. In
fact, all current CMOS setup utilities seem to autodetect CD-media ATAPI
drives. If you go into CMOS after
installing a CD-ROM drive as mas-
ter on the secondary IDE controller,
for example, the drive will show up
just fine, as in Figure 8.52.
The  reporting  of  installed
CD-media drives in CMOS serves
two purposes. First, it tells the tech-
nician that he or she has good con-
nectivity on the ATAPI drive.
Second, it shows that you have the
option to boot to CD-media, such as
a Windows XP disc. What it doesn't
do, however, is provide true BIOS
support for that drive! That has to
come with a driver loaded at
Figure 8.52  CMOS screen showing a CD-ROM drive detected
Chapter 8: Hard Drive Technologies
Troubleshooting Hard Drive
The best friend a tech has when it comes to troubleshooting hard drive in-
stallation is the autodetection feature of the CMOS setup utility. When a
The CompTIA A+ 220-603
drive doesn't work, the biggest question, especially during installation, is,
exam is interested in trouble-
"Did I plug it in correctly?" With autodetection, the answer is simple; if it
shooting storage devices, but
doesn't see the drives, something is wrong with the hardware configura-
more from the software side
tion. Either a device has physically failed or, more likely, you didn't give the
than the physical installation
hard drive power, plugged a cable in backwards, or messed up some other
connectivity issue.
It takes four things to get a drive installed and recognized by the system:
jumpers (PATA only), data cable, power, and CMOS setup recognizing the
drive. If any of these steps is missed or messed up, you have a drive that
simply doesn't exist according to the PC! To troubleshoot hard drives, sim-
ply work your way through each step to figure out what went wrong.
First, set the drive to master, slave, standalone, or cable select, depend-
ing on where you decide to install the drive. If a drive is alone on the cable,
set it to master or standalone. With two drives, one must be master and the
other slave. Alternatively, you can set both drives to cable select and use a
cable-select cable.
Second, the data cable must be connected to both the drive and control-
ler, Pin 1 to Pin 1. Reversing the data cable at one end is remarkably easy to
do, especially with the rounded cables. They obviously don't have a big red
stripe down the side to indicate the location of Pin 1! If you can't autodetect
the drive, check the cabling.
Third, be sure to give the hard drive power. Most hard drives use a stan-
dard Molex connector. If you don't hear the whirring of the drive, make cer-
tain you plugged in a Molex from the power supply, rather than from
another source such as an otherwise disconnected fan. You'd be surprised
how often I've seen that!
Fourth, you need to provide BIOS for the controller and the drive. This
can get tricky as the typical CMOS setup program has a lot of hard drive op-
tions. Plus, you have an added level of confusion with RAID settings and
non-integrated controllers that require software drivers.
Once you've checked the physical connections, run through these issues
in CMOS. Is the controller enabled? Is the storage technology--LBA, INT13,
ATA/ATAPI-6--properly set up? Similarly, can the motherboard support
the type of drive you're installing? If not, you have a couple of options. You
can flash the BIOS with an upgraded BIOS from the manufacturer or you
can get a hard drive controller that goes into an expansion slot.
Finally, make certain with non-integrated hard drive controllers, such as
those that come with many SATA drives, that you've installed the proper
drivers for the controller. Driver issues can crop up with new, very large
drives, and with changes in technology. Always check the manufacturer's
Web site for new drivers.
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Beyond A+
Spindle (or Rotational) Speed
Hard drives run at a set spindle speed, measured in revolutions per minute
(RPM). Older drives run at the long-standard speed of 3600 RPM, but new
drives are hitting 15,000 RPM! The faster the spindle speed, the faster the
controller can store and retrieve data. Here are the common speeds: 4500,
5400, 7200, and 10,000 RPM.
Faster drives mean better system performance, but they can also cause
the computer to overheat. This is especially true in tight cases, such as
minitowers, and in cases containing many drives. Two 4500 RPM drives
might run forever, snugly tucked together in your old case. But slap a hot
new 10,000 RPM drive in that same case and watch your system start crash-
ing right and left!
You can deal with these hotrod drives by adding drive bay fans between
the drives or migrating to a more spacious case. Most enthusiasts end up do-
ing both. Drive bay fans sit at the front of a bay and blow air across the drive.
They range in price from $10 to $100 (U.S.) and can lower the temperature of
your drives dramatically. Figure 8.53 shows a picture of a double-fan drive
bay cooler.
Air flow in a case can make or break your system
stability, especially when you add new drives that
increase the ambient temperature. Hot systems get
flaky and lock up at odd moments. Many things can
impede the air flow--jumbled up ribbon cables,
drives squished together in a tiny case, fans clogged
by dust or animal hair, and so on.
Technicians need to be aware of the dangers
when adding a new hard drive to an older system.
Get into the habit of tying off ribbon cables, adding
front fans to cases when systems lock up intermit-
tently, and making sure the fan(s) run well. Finally,
if a client wants a new drive and his system is a tiny
minitower with only the power supply fan to cool it
off, be gentle, but definitely steer him to one of the
slower drives!
Figure 8.53  Bay fans
Hybrid Hard Drives
Windows Vista supports hybrid hard drives (HHDs), drives that combine
flash memory and spinning platters to provide fast and reliable storage.
Samsung has drives with 128-MB and 256-MB flash cache, for example, that
shave boot times in half and, because the platters don't have to spin all the
time, add 20­30 minutes more of battery life for portable computers. Add-
ing that much more run time with only a tiny price premium and no extra
weight is the Holy Grail of portable computing!
Chapter 8: Hard Drive Technologies
Chapter 8 Review
Chapter Summary
After reading this chapter and completing the
geometric values, have no relevance in today's
exercises, you should understand the following about
PCs, but most CMOS utilities still support them.
hard drive technologies.
ATA--The King
How Hard Drives Work
Today's hard drives have either an ATA interface
or a SCSI interface. ATA drives may be parallel
Hard drives contain aluminum platters coated
ATA (PATA) or the newer serial ATA (SATA).
with a magnetic medium and read/write heads
A specification of the American National
that float on a cushion of air. Hard drives store
Standards Institute (ANSI), the AT Attachment
data in a tiny magnetic field called a flux that
(ATA) interface (commonly but incorrectly referred
defines a zero or a one. The switching back and
to as IDE) used a 40-pin ribbon cable, had a built-in
forth of the field is called flux reversal. The
controller, and did not require a low-level format.
incredible storage capacity of today's drives is due
By 1995, EIDE was the dominant interface. Its
to Partial Response Maximum Likelihood (PRML)
features include higher capacities, support for
encoding that includes intelligent circuitry to
non­hard drive storage devices, a four device
analyze each flux reversal.
maximum, and improved throughput. The terms
Two different technologies have been used to move
ATA, IDE, and EIDE are used interchangeably to
read/write heads across the platters: stepper
describe all PATA devices.
motors and voice coil. Very susceptible to physical
deterioration and temperature changes, the now
PATA drives use a 40-pin plug and a controller that
obsolete stepper motors moved the actuator arm in
connects them to the external data bus. Although
fixed increments or steps, often resulting in data
the real controller is built into the hard drive itself,
transfer errors or the inability to access data on a
the 40-pin connector on the motherboard is
cold drive. The heads had to be parked to a
called the controller. Most modern motherboards
non-data area when not in use to prevent possible
contain two PATA controllers, each capable of
damage to the disk surface. Today's drives use a
supporting up to two PATA devices. By looking at
linear or voice coil motor consisting of a permanent
the motherboard itself or at the motherboard book,
magnet surrounding a coil on the actuator arm.
you can determine which is the primary controller
Electrical current causes the coil to generate a
and which is the secondary. If you are using only
magnetic field that moves the actuator arm and
one controller, it should be the primary one.
thus the read/write heads. Containing no data, one
The Advanced Technology Attachment Packet
side of one platter is used as a map to position the
Interface (ATAPI) enables non­hard drive devices
heads directly over the data. Voice coil technology
to use a PATA controller. ATAPI devices, such as
automatically parks the heads when the drive loses
CD-ROM drives, use the same 40-pin interface and
follow the same rules of master, slave, and cable
select jumper settings. Non­hard drives must get
Disk geometry for a particular hard drive consists of
their BIOS from option RAM or a software driver.
three primary values: heads, cylinders, and sectors
per track. There are two read/write heads per
Originally, IDE drives used the same BIOS command
platter. A hard drive can have either an even or an
set introduced years earlier. Maximum values of
odd number of heads. A cylinder defines a group of
1024 cylinders, 16 heads, and 63 sectors per track
tracks of the same diameter. Each track is sliced into
limited an IDE drive's capacity to 528 million bytes
tiny slivers called sectors, each of which stores
(504 MB). Western Digital developed the LBA
512 bytes of data. Disk geometry uses the number of
sector translation method to accommodate larger
sectors per track. Combining cylinders, heads, and
EIDE drives. LBA supports drives with up to
sectors per track is referred to as CHS. Write
256 heads, for a storage capacity limit of 8.4 GB.
precompensation and landing zone, two other
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
As drive capacity neared the 8.4-GB maximum,
All SCSI devices can be divided into two groups:
Phoenix Technologies broke the limit by coming up
internal and external. Internal SCSI devices connect
with a new set of BIOS commands called Interrupt
to the host adapter with a 68-pin ribbon cable.
13 extensions (INT13). Completely ignoring the CHS
External devices connect to the host adapter with
values, INT13 supports drives up to 137 GB by
either a 50-pin HD connector or a 68-pin HD
reporting a stream of "addressable sectors" to LBA.
connector. SCSI enables you to daisy-chain devices
together to form longer SCSI chains.
As drive capacity neared the 137-GB limit, the
ANSI ATA committee adopted ATA/ATAPI-6, a
Improper termination or incorrect SCSI ID settings
new standard that increased the limit to more than
are the two most common causes of SCSI devices
144 petabytes (144,000,000 GB). It uses a 48-bit
not working. The key factor here is that you must
addressing scheme and an enhanced block mode
terminate only the ends of the SCSI chain.
that transfers up to 65,536 sectors at a time.
Protecting Data with RAID
Newer hard drives use direct memory access
Drive mirroring writes data simultaneously to two
(DMA) mode to send data directly to RAM,
hard drives, enabling the system to continue to
bypassing the CPU. Instead of using the slow
work if one hard drive dies. A faster and even
DMA controller chip, today's DMA transfers use
more effective technique is drive duplexing, which
bus mastering to transfer 32 bits of data. Hard
performs mirroring using separate controllers for
drives typically use one of the following modes:
each drive. A third way to create redundant data is
Ultra DMA mode 4 (ATA/66), Ultra DMA mode 5
disk striping with parity. This technique, requiring
(ATA/100), and Ultra DMA mode 6 (ATA/133).
at least three drives, combines the redundancy of
To use Ultra DMA, you must have a controller and
disk mirroring with the speed of disk striping.
an 80-wire ribbon cable. Some motherboards
Although disk striping without parity works very
combine different speeds of ATA controllers, with
fast, splitting the data across two drives means
the higher speed controller indicated with a bright
you'll lose all data if either drive fails.
color. The 80-wire ribbon cable indicates where the
master and slave drives should be connected.
Numbered 0 through 6, there are seven official
High-end PATA devices can use lower end
levels of RAID, but the most commonly used ones
controllers, but they will operate at the slower
are RAID 0 (disk striping), RAID 1 (disk mirroring
or duplexing), and RAID 5 (disk striping with
distributed parity).
Serial ATA (SATA) devices look identical to
standard PATA devices (except their data and
RAID may be implemented through hardware or
power connectors), but their thinner seven-wire
software methods. While software implementation is
cables provide better airflow and may be up to a
cheaper, hardware techniques provide better
meter (39.4 inches) long. SATA does away with the
performance. Windows 2000 Server and Windows
entire master/slave concept. Each drive connects to
2003 Server include built-in RAID software for
one port, so no more daisy-chaining drives.
RAID 0, RAID 1, and RAID 5 for either ATA or SCSI.
Windows 2000 and XP Professional include Disk
SATA devices are hot-swappable, great for RAID
Management for RAID 0. RAID software solutions
technology. SATA transfers data in serial bursts,
tend to overwork your operating system, resulting in
for up to 30 times the throughput of PATA. SATA
slowdowns. Hardware RAID is invisible to the OS and
drives come in two common varieties, the 1.5Gb
is usually hot-swappable. A hardware ATA RAID
and the 3Gb, that have a maximum throughput of
controller usually requires CMOS configuration. Many
150 MBps and 300 MBps, respectively.
motherboards include built-in ATA-based hardware
RAID 0 and RAID 1 capabilities.
SCSI: Still Around
All SCSI chains, which support either 8 or 16
SCSI drives were a natural for the multiple-disk
devices including the controller, require proper
RAID. Specialized ATA RAID controller cards
termination to prevent signal echo. Additionally,
support ATA RAID arrays of up to 15 drives. With
each device on a chain requires a unique SCSI ID,
its hot-swap capabilities, SATA may soon take over
which can be set by jumpers, switches, or dials.
lower end RAID from SCSI.
Chapter 8: Hard Drive Technologies
Connecting Drives
autodetection does not provide true BIOS support.
You must still install drivers to provide the BIOS. If
Older PATA drives use a 40-wire cable, while the
the driver is installed in a graphical mode, you will
newer Ultra DMA drives use an 80-wire cable.
be unable to access the drive if you boot to a
Either round or flat and containing no twists, each
command prompt­only environment.
ribbon cable supports two drives. A diagram on
the hard drive's housing shows how to set its
It takes four things to get a drive installed and
jumpers to identify it as master, slave, standalone
recognized by the system: jumpers, data cable,
(on some drives), or cable select (cable position
power, and CMOS setup or providing BIOS. If any
determines whether the drive will be master or
of these steps is missed or messed up, your drive
slave). Two devices on one cable must both be set
simply doesn't exist according to the PC.
to cable select, and the cable itself must also be
If the autodetection feature of the CMOS utility
cable select, as indicated with a pinhole through
does not detect a drive, it means it is installed
one wire. Align the colored stripe on the cable with
incorrectly or the drive itself is bad. Check the
pin 1 on the controller and the drive. Use a Molex
master/slave jumper settings. Make sure that the
connector to provide power to the drive.
ribbon cable aligns pin 1 with pin 1, and that the
SATA supports only a single device per controller
Molex connector is supplying power to the drive.
channel, so there are no master, slave, or cable
Once you've checked the physical connections, run
select jumpers. SATA controller and power cables
through these issues in CMOS. Is the controller
are keyed to prevent incorrect insertion. You can
enabled? Is the storage technology--LBA, Large,
connect a PATA device to a SATA motherboard
INT13, ATA/ATAPI-6--properly set up? What
controller by way of a SATA bridge.
about the data transfer settings for PIO and DMA
modes? Similarly, can the motherboard support the
BIOS Support: Configuring CMOS
type of drive you're installing? If not, you can flash
and Installing Drivers
the BIOS or get a hard drive controller that goes
While system BIOS supports built-in PATA
into an expansion slot. Make certain with
controllers, hard drives require configuration in
non-integrated hard drive controllers, such as
CMOS. ATAPI devices require software drivers to
those that come with many SATA drives, that
provide BIOS support. Built-in SATA controllers
you've installed the proper drivers for the
on a motherboard also require software drivers, as
controller. Always check the manufacturer's Web
does a SATA controller on a separate expansion
site for new drivers.
card. All SATA devices get BIOS support from the
SATA controller, but some drives require
Troubleshooting Hard Drive Installation
additional configuration; in particular, with RAID
It takes four things to get a drive installed and
systems, you may also have to configure the
recognized by the system: jumpers (PATA only),
controller Flash ROM settings for the specific
data cable, power, and CMOS setup recognizing
drive(s) you install.
the drive. If any of these steps is missed or messed
When the hard drive type is set to "Auto," PATA
up, you have a drive that simply doesn't exist
devices can be queried directly by BIOS routines,
according to the PC! To troubleshoot hard drives,
resulting in the correct CMOS settings for up to
simply work your way through each step to figure
four ATA devices. Autodetection made hard drive
out what went wrong.
types obsolete. Because PATA drives have CHS
Once you've checked the physical connections, run
values stored inside them, the BIOS routine, when
through these issues in CMOS. Is the controller
set to "Auto," updates the CMOS each time the
enabled? Is the storage technology--LBA, INT13,
computer boots. An alternative is to run the
ATA/ATAPI-6--properly set up? Similarly, can
autodetection option from the CMOS screen.
the motherboard support the type of drive you're
Even if the autodetect feature indicates that an
installing? If not, you have a couple of options. You
optical ATAPI drive has been installed, this merely
can flash the BIOS with an upgraded BIOS from
shows that the drive is connected properly and has
the manufacturer or you can get a hard drive
the option to function as a boot device. This
controller that goes into an expansion slot.
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Key Terms
40-pin ribbon cable (109)
geometry (105)
SCSI chain (120)
80-wire cable (116)
heads (105)
SCSI ID (122)
Advanced Technology Attachment
integrated drive electronics
sector (106)
Packet Interface (ATAPI) (114)
(IDE) (108)
sector translation (113)
ATA/133 (118)
Interrupt 13 (INT13)
sectors per track (107)
extensions (116)
ATA/ATAPI-6 or simply
Self-Monitoring, Analysis, and
ATA-6 (117)
logical block addressing
Reporting Technology
(LBA) (112)
cylinder (106)
(S.M.A.R.T.) (115)
PIO modes (111)
disk duplexing (124)
serial ATA (SATA) (108)
parallel ATA (PATA) (108)
disk mirroring (124)
small computer system interface
(SCSI) (120)
Partial Response Maximum
disk striping (124)
Likelihood (PRML) (103)
stepper motor (104)
disk striping with parity (126)
redundant array of independent
termination (123)
DMA modes (111)
(or inexpensive) disks
track (106)
Enhanced IDE (EIDE) (111)
(RAID) (126)
Ultra DMA (116)
External SATA (eSATA) (120)
SATA bridge (119)
voice coil (104)
Key Term Quiz
Use the Key Terms list to complete the sentences that
5. Seen in RAID 5, ____________ uses at least three
follow. Not all terms will be used.
drives and combines the best features of disk
mirroring and disk striping.
1. An ATA hard drive connects to the controller
6. A(n) ____________-compliant CD-ROM drive
with a(n) ____________ while an Ultra DMA
installs and cables just like an EIDE drive.
drive uses a(n) ____________.
7. The ANSI ATA committee adopted the
2. A(n) ____________ is composed of a group of
____________ standard, called "Big Drives" by
tracks of the same diameter that the read/write
Maxtor, that allows drives with more than 144
heads can access without moving.
3. To install a parallel ATA device to a serial ATA
8. ____________ drives transfer data at 133 MBps.
controller, use a tiny card called a(n)
9. Drives that use ____________ bypass the CPU
and send data directly to memory.
4. LBA, developed by Western Digital, uses
10. ____________ devices require termination at both
____________ to get around the limits of 1024
ends of a chain.
cylinders, 16 heads, and 63 sectors/track.
Multiple-Choice Quiz
1. Which of the following is NOT used to compute
2. Which level of RAID is disk striping with
storage capacity in CHS disk geometry?
distributed parity?
A. Sectors per track
B. Tracks
C. Heads
D. Cylinders
Chapter 8: Hard Drive Technologies
3. Which of the following is the most efficient
encoding method?
A. Partial Response Maximum Likelihood (PRML)
B. Frequency modulation (FM)
C. Run length limited (RLL)
9. Shelby wants to add a new 100-GB hard drive to
her computer. Which of the following will allow
D. Modified frequency modulation (MFM)
her to do so?
4. Counting both channels, what is the maximum
number of drives/devices that EIDE can
A. One
B. Two
D. INT13
C. Seven
10. Which of the following techniques provides
redundancy by using two disks and two
D. Four
5. Which of the following is NOT true about cable
A. Drive mirroring
B. Drive duplexing
A. Both drives/devices should be set for cable
C. Disk striping
B. It requires a special cable with a pinhole
D. Disk striping with parity
through one wire.
11. How many wires does an Ultra DMA cable
C. The colored stripe on the ribbon cable should
align with pin 1 on the controller and drive.
A. 24
D. Position of the drives on the cable does not
B. 34
C. 40
6. If you install two IDE drives on the same cable,
D. 80
how will the computer differentiate them?
12. Billy just installed a second hard drive, but the
A. The CMOS setup allows you to configure
autodetection utility in CMOS does not detect it.
Sara told him he probably had the jumpers set
B. You must set jumpers to determine which
incorrectly or had forgotten to connect the Molex
drive functions as master and which
power connector. John told him his new hard
functions as slave.
drive is probably bad and he should return it. Is
C. You will set jumpers so each drive will have a
Sara or John probably correct?
unique ID number.
A. Sara is correct.
D. The drives will be differentiated by whether
B. John is correct.
you place them before or after the twist in the
C. Neither is correct.
ribbon cable.
D. Either John or Sara may be correct.
7. What was the maximum hard drive size allowed
13. Which of the following is NOT an advantage of
by BIOS routines for the original AT command
serial ATA (SATA)?
A. It is hot-swappable.
A. 528 MB
B. Thinner cables provide better airflow inside
B. 1024 MB
the case.
C. 504 MB
C. SATA provides faster data throughput than
D. 1028 MB
8. Which of the following terms does NOT describe
D. SATA cable must be shorter than PATA
parallel ATA devices?
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
14. Which of the following two CMOS configuration
15. What standard did the ANSI ATA committee
options are obsolete with today's hard drives?
adopt that increased disk storage capacity to
more than 144 petabytes?
A. Cylinders and heads
B. Heads and sectors
C. Sectors and write precompensation
C. INT13
D. Write precompensation and landing zone
Essay Quiz
1. Discuss at least three advantages of serial ATA
features including storage capacity, interface,
over parallel ATA.
RPM, and cost:
2. Compare and contrast hardware and software
Maxtor Model # 6Y120L0 and Maxtor Model
RAID implementation.
# 6Y120M0
3. Your friend Blaine has a Pentium III computer
Western Digital Model # WD1200JB and
with a 100-MHz bus. Currently, it has only a
Western Digital Model # WD1200JD
20-GB ATA/100 hard drive and a CD-RW drive.
Since he's interested in graphics, he knows he
5. Hard drives include other features and
needs more storage capacity and wants to add a
characteristics not included in this chapter.
second hard drive. What advice will you give
Choose one of the following topics and use the
him about selecting a new hard drive?
Internet to define and explain it to the class.
4. Use www.google.com or a site such as
Zone bit recording
www.newegg.com to compare one of the
"Pixie dust" hard drives
following pairs of hard drives to determine their
Lab Projects
Lab Project 8.1
Access the CMOS setup for your computer and
utility and run it. Does it offer different modes with
examine the settings that apply to your hard drive(s)
different drive capacities? Try to find a screen that
and EIDE interface. In particular, look at the initial
includes PIO modes and examine this setting. What
screen to see if it is set to autodetect the kind of hard
other screens apply to the hard drive? When you
drive. Is the mode set to LBA or something else?
finish, be sure to choose Quit without Saving.
Now find the screen that includes the autodetect
Lab Project 8.2
Visit your local computer store or use the Internet to
parallel ATA interfaces or if they offer serial ATA
discover what kinds of hard drives and hard drive
interfaces, either onboard or through an expansion
interfaces are commonly offered with a new computer.
card. If you were purchasing a new computer, would
Try to determine whether the motherboards offer only
you select PATA or SATA? Why?
Chapter 8: Hard Drive Technologies
Lab Project 8.3
Your supervisor has decided to implement RAID on
security of data at the lowest cost possible, and the
the old company server machine, where everyone
other that maximizes speed but retains some
stores their work-related data. Come up with two
security. Cost is not a factor for the second RAID
competing RAID setups, one that maximizes
Lab Project 8.4
If your lab has the equipment, install a second hard
detected. Boot into your operating system and verify
drive in your system. Install it on the same cable as
that both drives are accessible. (You may need to
the existing drive and jumper it as the slave. (You
partition and format the second drive before it is
may need to jumper the existing drive as master.)
actually usable.)
Reboot, enter CMOS, and verify both drives are
Mike Meyers' CompTIA A+ Guide: PC Technician (Exams 220-602, 220-603, & 220-604)
Table of Contents:
  1. Computer Architecture, Organization and Design
  2. Foundations of Computer Architecture, RISC and CISC
  3. Measures of Performance SRC Features and Instruction Formats
  4. ISA, Instruction Formats, Coding and Hand Assembly
  5. Reverse Assembly, SRC in the form of RTL
  6. RTL to Describe the SRC, Register Transfer using Digital Logic Circuits
  7. Thinking Process for ISA Design
  8. Introduction to the ISA of the FALCON-A and Examples
  9. Behavioral Register Transfer Language for FALCON-A, The EAGLE
  10. The FALCON-E, Instruction Set Architecture Comparison
  11. CISC microprocessor:The Motorola MC68000, RISC Architecture:The SPARC
  12. Design Process, Uni-Bus implementation for the SRC, Structural RTL for the SRC instructions
  13. Structural RTL Description of the SRC and FALCON-A
  14. External FALCON-A CPU Interface
  15. Logic Design for the Uni-bus SRC, Control Signals Generation in SRC
  16. Control Unit, 2-Bus Implementation of the SRC Data Path
  17. 3-bus implementation for the SRC, Machine Exceptions, Reset
  18. SRC Exception Processing Mechanism, Pipelining, Pipeline Design
  19. Adapting SRC instructions for Pipelined, Control Signals
  20. SRC, RTL, Data Dependence Distance, Forwarding, Compiler Solution to Hazards
  21. Data Forwarding Hardware, Superscalar, VLIW Architecture
  22. Microprogramming, General Microcoded Controller, Horizontal and Vertical Schemes
  23. I/O Subsystems, Components, Memory Mapped vs Isolated, Serial and Parallel Transfers
  24. Designing Parallel Input Output Ports, SAD, NUXI, Address Decoder , Delay Interval
  25. Designing a Parallel Input Port, Memory Mapped Input Output Ports, wrap around, Data Bus Multiplexing
  26. Programmed Input Output for FALCON-A and SRC
  27. Programmed Input Output Driver for SRC, Input Output
  28. Comparison of Interrupt driven Input Output and Polling
  29. Preparing source files for FALSIM, FALCON-A assembly language techniques
  30. Nested Interrupts, Interrupt Mask, DMA
  31. Direct Memory Access - DMA
  32. Semiconductor Memory vs Hard Disk, Mechanical Delays and Flash Memory
  33. Hard Drive Technologies
  34. Arithmetic Logic Shift Unit - ALSU, Radix Conversion, Fixed Point Numbers
  35. Overflow, Implementations of the adder, Unsigned and Signed Multiplication
  36. NxN Crossbar Design for Barrel Rotator, IEEE Floating-Point, Addition, Subtraction, Multiplication, Division
  37. CPU to Memory Interface, Static RAM, One two Dimensional Memory Cells, Matrix and Tree Decoders
  38. Memory Modules, Read Only Memory, ROM, Cache
  39. Cache Organization and Functions, Cache Controller Logic, Cache Strategies
  40. Virtual Memory Organization
  41. DRAM, Pipelining, Pre-charging and Parallelism, Hit Rate and Miss Rate, Access Time, Cache
  42. Performance of I/O Subsystems, Server Utilization, Asynchronous I/O and operating system
  43. Difference between distributed computing and computer networks
  44. Physical Media, Shared Medium, Switched Medium, Network Topologies, Seven-layer OSI Model