HARD DISK DRIVE GUIDE
HOW A HARD DISK DRIVE WORKS?
Last updated: 6/2/00
 A
hard disk drive consists of a motor, spindle, platters, read/write heads,
actuator, frame, air filter, and electronics. The frame mounts the
mechanical parts of the drive and is sealed with a cover. The sealed
part of the drive is known as the Hard Disk Assembly or HDA. The drive
electronics usually consists of one or more printed circuit boards mounted
on the bottom of the HDA.
A head and platter can be visualized as being similar to
a record and playback head on an old phonograph, except the data structure
of a hard disk is arranged into concentric circles instead of in a spiral
as it on a phonograph record (and CD-ROM). A hard disk has one or more
more platters and each platter usually has a head on each of its sides. The
platters are mounted on the spindle which is turned by the drive motor. Most
current IDE hard disk drives spin at 5,400 or 7,200 RPM and 10,000 RPM drives
are emerging. A layer of magnetic material is deposited on the surface
of the platters and those in most of the drives I've dissected have shiny,
chrome-like surfaces.
The heads (or Winchester sliders) are spring-loaded airfoils
and actually fly like an airplane above (or below) the surface of the platters
at a distance measured in micro-inches. This sort of mechanism is known
as a Winchester hard disk drive and was invented by IBM in 1973.  The
heads are extremely small electromagnets and are shown schematically to the
right (for a prettier and more detailed picture with separate read and write
elements, click here). Information
is stored on the platters by sending pulses of current from the drive electronics
to the head. The direction of the current and thus the direction of
the diverging magnetic field across the gap in the head determines the direction
the magnetic domains (little bitty, molecular magnets) on a particular spot
on the platter's magnetic coating, and, thus, whether the spot represents
a binary one or zero. The domains essentially retain their directional bent
(whether the computer is on or off) until "told" to do otherwise
by the drive electronics, which take their orders from the rest of the computer
and ultimately from software. The complexity of the mechanisms and
methods associated with doing all of this will be omitted here.
 The
heads move together and are propelled across the disk surface by the actuator. The
actuator on most recent hard disks employs a voice coil mechanism. It
functions much like the voice coil in a loud speaker, thus its name. It
consists of a curved magnet (or magnets--very strong ones) and a spring-loaded
coil of fine wire which is attached to the read/write heads by head arms. The
head arms are attached to, and pivot about an actuator shaft. When
the drive electronics apply an electric current to the actuator coil, it
interacts with the magnet and swings against the actuator spring. The
heads rotate around the actuator shaft in the opposite direction of the coil
movement, inward and outward from the center to the edges of the platters. If
there is a power outage the spring, which counterbalances the the electromagnetic
force between the coil and magnet, takes over and automatically parks (lands
them on skids or nanosliders--like pontoons on a sea plane) and locks the
heads on a part of the platters called a landing zone (like an airport runway
only curved) before they can crash (like an airplane) on, and mar that part
of the surface of the platters where data is stored. When power is
restored, the platters speed-up and the heads take off (like a tethered model
airplane, except the ground moves--and those on the bottoms of the platters
can fly up-side-down) and start flying again--an extraordinary mechanism...
One no longer has to park a hard disk before moving
the computer as was the case in times of old when actuators were moved
by devices known as stepper motors. However, if the power jitters
repeatedly or the drive is subjected whack from a frustrated user, a
crash can occur.
 Try
to visualize a thin, hollow cylinder passing through all of the platters. It
would produce a circular track on each side of each platter. Now divide
each tack into equal arcs or sectors. Well, that is exactly how a hard
disk is organized. That is, Cylinders, Heads (which are equal the number
of tracks or platter sides), and Sectors are the coordinates of the data
on a hard disk drive.
SERVO-FORMATTING. There are two kinds of sectors
on a hard disk. The first and at the very lowest level is a servo sector. When
a hard disk is manufactured a special pattern is written in a code called
a Gray code on the surface of the platters, while the drive is open in a
clean room, with an expensive machine called a servowriter. Although
there are other schemes, it is written in a wedge at the start of each
sector (an embedded servo pattern) on most drives. There are a fixed
number of servo sectors per track and the sectors are adjacent to one another. This
pattern is permanent and cannot be changed by writing normal data to the
drive. It also cannot be changed by low-level formatting (see below) the
drive, as some may think. If it is changed, the drive has had it--kaput! The
electronics use feedback from the heads, which read the Gray code pattern,
to very accurately position, and constantly correct the radial position of
the appropriate head over the desired track, at the beginning of each sector,
to compensate for variations in platter geometry, caused by mechanical stress
and thermo expansion and contraction. Altogether, the head positioning
components form what is know as closed loop servo system--a marvelous (and,
perhaps, dangerous) thing to watch operate in a drive which has been opened.
LOW-LEVEL FORMATTING. After the servowriter
has done its thing and the drive is sealed, the hard disk drive is low-level
formatted to create the second level of sectors: data sectors. The
servo sectors are divided into data sectors. Current IDE drives employ
zoned-bit recording which varies the number of data sectors per track. Servo
sectors in outer tracks are divided into more data sectors than those in
the the inner tracks. In the interest of keeping things simple we will
not digress further into zoned-bit recording and will maintain the conceptual
model of a fixed number of sectors per track established by the above diagram. Furthermore,
the drive firmware further translates the physical cylinders, heads,
and data sectors back and forth into a different combination of cylinders,
heads and cylinders, as seen by the computer, so they fall within the constraints
of the various operating systems. What you will see (and what the computer
sees) when you work with the drive is a simpler fixed number of sectors per
track. Below the surface things are much more complex. And the
diagram of the hard disk platter above is necessarily greatly simplified. In
reality the coding. etc. is much more complex then discussed here, and there
are many more tracks and sectors on modern hard disk drives--you certainly
cannot see them.
Gaps from Mueller--> Low-level formatting creates and
demarcates data sectors (or blocks)--writes to the servo sectors and puts
spaces between the data sectors. This together with servo formatting
allows the heads to read and write data to and from the desired data sectors
as they whiz by.
Logical Geometry
Add more detail from Mueller et al--> Most
data sectors are about 600 bytes long and are divided into a prefix region,
a data region, and a suffix region. 512 bytes are used for data. The
low-level format writes format information to the sector prefixes and suffixes. The
prefix region identifies the start of a sector and contains its number. Most
hard disks have defects on their platters where data cannot be reliably stored. The
low-level formatting process detects these defects in a write/read
surface scan of the drive, saves them in a defect list identifying the offending
sectors, and writes bad sector information into the suffix regions of viable
sectors--marks bad sectors as such. A check-sum used to verify the
data in the data area is recorded in the suffix region of good sectors. A
fixed value is repeatedly written to the data region.
In the "old days," we had to low level-format
all hard disk drives and manually enter the defect list using the DOS
debug program to talk to the controller's BIOS.
All current IDE drives are low-level formatted when manufactured
and should not require a low-level format again. It shouldn't be attempted
on modern drives unless specifically directed by the manufacture's representatives. An
unusable drive can result. In many cases manufacturer-specific software/hardware
has to be used to low-level format a hard disk drive.
Electronics - cache'
In summary, when we buy a new hard disk drive it
has been servo formatted, low-level formatted, and otherwise "magically" transformed
by the manufacturer and electronics into a "black box" with its
cylinders, heads, and sectors printed on a label on the top of the drive. Those
parameters are pretty much "fixed in concrete," and they are what
we deal with when installing a hard disk drive.
LARGE BLOCK ADDRESSING (LBA). Most operating
systems (e.g., Windows) are limited in the maximum number of cylinders and
sectors they can address. Most modern hard disk drives exceed those
limitations. Most computer BIOS's (Basic Input Output System--a program
on a chip on the motherboard which manages the computer's innards below the
operating system) couldn't care less. Most current motherboard BIOS's
solve this problem with LBA.
HOMEWORK. Before plunking-down the cash
to buy that new hard disk, it is advisable to do some homework. First,
check with the motherboard manufacture's web site to see if will support
the hard disk. Some older computers have a problem with drives greater
than 8.4 GB. The BIOS may need to be flashed or replaced. If you BIOS
LBA
If your version of Windows older than Windows 95 OSR2 (see http://duxcw.com/digest/Howto/software/winver.htm),
you will have to divide your drive into 2 GB partitions (see below) each
with a logical drive (C:,D:,E:, F:, and G:). If you have an old version of
Win 95, now is probably a good time to upgrade to Win 98/98 SE.
Determine if you have a place to mount the drive in your
computer. If you only have 5 1/4" drive bays open, you may need
a 3 1/2" to 5 1/4" mounting kit.
Your new drive and old drive should be installed on the
same cable, the one going to the primary IDE interface on the motherboard.
If one of the drives is put one the same cable as your CD-ROM, the CD-ROM
could slow it down. Is the cable long to reach both drives? You can plug
either end of the cable into motherboard (in fact, you can plug anyone of
the three connectors into the motherboard. The cable does have three connectors,
doesn't it? The cable should not exceed 16” in length. The red stripe goes
towards pin 1 on the motherboard and drives. Check to see if you have enough
drive power connectors on the power supply. You may need a Y connector. Obtain
the jumper settings from the manufacture’s web site for your old drive if
they aren’t on the drive itself. I would run a virus scan on the old drive
and any floppies used to install software.
Your new drive should be your C: drive. It is probably
faster and is newer than your old drive. If you decide to make the new drive
your C: drive, you need to decide if you are going to move everything from
the old drive to the new one or do a complete reinstall. A new install
is probably best, but that means you will have to reinstall all of your old
software and hardware drivers. You will need to be sure that you have all
of software and drivers to do that. You may want to download all of the most
recent drivers for your hardware to you old hard disk where they will be
available during the final installation on your new drive. If you are going
to copy your old drive to your new one, you should obtain and learn how use
a software utility, such as Partition Magic (http://www.powerquest.com/partitionmagic/index.html)
or Ghost,
capable of copying an image of your old drive to your new one. XCOPY just
does not do a good job of coping Windows to a new drive.
 I’ll
assume you have decided to install your new drive as the C: drive and do
a new install of Windows. Read the following articles for instructions:
http://duxcw.com/digest/Howto/software/windows/upgrade/intro.htm
http://duxcw.com/digest/Howto/software/windows/cabs/movecabs.htm
http://duxcw.com/digest/Howto/buildcom/athlon/index.html (Parts
5,6,7, and 8)
Be sure you old drive is completely disconnected when doing
this so you won’t accidentally scrub your old drive and that your new drive
is jumpered for Master with no Slave present. Set your CMOS to auto detect
the C: drive. After parting, formatting, and installing Windows, shutdown
the computer, jumper the new drive as a Master with Slave present (some drives
like Maxtor don’t have this setting and no change is required), the old drive
as a Slave, connect both drives, and boot-up the new drive to Windows. Be
sure your Windows Explorer is configured to show hidden folders and files
and use it to copy everything from the old drive except the root (\) directory
and the Windows Directory (folder). You can also search for and copy your
Internet favorites and cookies from the Windows folder on your old drive
to corresponding folders on your new drive. Reinstall all of your software
and Internet configuration. The software should find your data if you reinstalled
in the default/same locations. Guess with a little more work I’ll have my
article… I hope this helps and that others will extend their advice.
I would leave the old drive alone for a while until you
are sure everything is working ok with the new one. You can then fdisk it
(be absolutely sure you have the right drive when doing this or disconnect
the new one and temporarily set the old one as a Master) for large disk support
(FAT32) if it was setup with an older version of Windows/DOS (FAT16) and
format it. It will then be useful for backing-up you data on the new drive
with Microsoft Backup which is included with windows (you may have to install
it as it not part of the default Windows install).
Windows 98 Second Edition (SE) OEM (Original
Equipment Manufacture--a company that builds computers, etc.) was installed
on this particular computer. I can see no reason why any version of
Windows 98 would not work.
Windows 95 should work also, but I have not
tested Windows 95 with a 650 Mhz Athlon processor (old
versions of Windows 95 do have a problem with AMD K6 CPUs which are faster
than 350 Mhz). Besides, because of the size of the hard disk, you
would want to use Windows
95 version OSR2 or later with large disk support (FAT32).
If you have an older version of Windows 95
or even Windows 3.X or Windows for Workgroups, you should be able to install
the Windows 98 or Windows 98 SE upgrade on this computer. See How
to Install the Windows 98 Upgrade on a New Hard Disk for instructions.
One can use an OEM Preinstall floppy to install
Windows 98 SE OEM on this computer. Or one can use a Windows
98 Startup Disk to install the OEM or upgrade versions of Windows
98/98 SE. Windows 95 OEM and upgrade versions can also be installed
in the same manner with appropriate OEM Preinstall or Startup floppies. Finally,
the Windows 98 OEM and Windows 98 SE OEM CDs are bootable and can be installed
without a Preinstall or Startup Disk with this motherboard. The CD
boots to the same menu found on the Startup Disk. The Windows 98/98
SE Upgrade CDs are not bootable.
HARD DISK PARTITIONS. Now, we are going to
jump out of basic theory into the realm of more immediately useful stuff,,,, A
third level of formatting, high-level formatting or disk operating system
(DOS) formatting, as described later in this article, must be done before
the drive can be used by Windows. However, before this "high-level" format
can be accomplished, the hard disk has to be defined so the operating system
(Windows, etc.) can use a program to format it. It has to be divided
into one or more areas known as partitions. When a hard disk is partitioned
information defining the beginning and ending cylinder, head, and sector
locations is written to the first sector on the hard disk; i.e., cylinder
0, head 0, and sector 0.
The first cylinder is physically located closest to
the spindle. Head 0 is on the top of the top platter. The
landing zone is the outermost cylinder.
The partition information is in the "boot sector," but
it is also known as the boot track, boot record, or master boot record. The
master boot program is also located on the boot sector. It reads the
partition information and transfers the boot-up process in the computer to
the partition on the hard disk which has been made "active." More
on that latter. Windows partitions are made with the FDISK.EXE
program which comes with Windows (and DOS, etc.).
More than one operating system can be put on a hard
disk (e.g., Windows and Linux) by making more than one partition and
putting an operating system on each one of them (see
our Windows FAQs). The operating system on the currently
active partition is the one that will boot.
I would suggest partitioning (see below) the
hard disk drive into at least two partitions for greater efficiency. It
would take an awfully long time to defrag a 27.3 GByte C: drive. The
hard disk in this computer was partitioned into a 4 GByte C: drive and the
remainder of the drive was partitioned as the D: drive.
1. Boot the computer from a Startup
Floppy or Directly from the Windows 98/98 SE OEM CD...
Startup floppy. Using the instructions
for making a Windows Startup Disk (I used the manual or custom
version of the floppy) make the floppy, put it in the floppy drive,
and turn on the computer. It should boot-up to the floppy drive
and display a menu (see below).
I did it this way because I already
have Startup Floppies as part of my shop tools. The Toshiba
DVD drive will work with the stock driver on the Startup Disk.
Win 98 CD. This is the
easiest thing to do for those you who do not have a Startup floppy . Turn
on the computer, press the Delete key to get into the CMOS Setup, select
Advance BIOS Features, press the Enter Key, Select First Boot device, use
the Page Up/Down keys to Select CDROM, Esc to the Main Menu, select Save & Exit
Setup, put the Windows 98 CD in the DVD drive, and press the Y key to exit
the CMOS Setup and reboot. The computer should boot to the following
menu:
-
Boot from Hard Disk
-
Boot from CD-ROM
Select 2.
The computer will boot to a second menu:
-
Start Windows 98 Setup from CD-ROM
-
Start Computer with CD-ROM support
-
Start Computer without CD-ROM support
If you booted from the floppy, it should display
a similar menu, depending on the method you used to make the Startup Disk.
In both cases, select 3.
If you select 1., the hard disk will
fdisk'd with one giant partition. It will reboot, format the drive,
and install Windows. This is not recommended for a drive this large
or for any drive over 4.3 GB.
The computer will display the DOS prompt on
drive A: (If you booted to the CD, A: is really part of the CD-ROM):
A:\>
2. Use FDISK to create
a new partition on your new hard disk as follows:
A:\>fdisk
Will produce the following screen:
Your computer has a disk larger than 512
MB. This version of Windows includes improved support for large disks,
resulting in more efficient use of disk space on large drives, and allowing
disks over 2 GB to be formatted as a single drive.
IMPORTANT: If you enable large disk support and create any new drives on
this disk, you will not be able to access the new drive(s) using other operating
systems, including some versions of Windows 95 and Windows NT, as well as
earlier versions of Windows and MS-DOS. In addition, disk utilities that
were not designed explicitly for the FAT32 file system will not be able
to work with this disk. If you need to access this disk with other operating
systems or older disk utilities, do not enable large drive support. [this
is usually not a problem]
Do you wish to enable large disk support (Y/N)...........? [Y]
3. Push the Enter key to accept the
default [Y] for FAT32. You will get the following menu:
FDISK Options
Current fixed disk drive: 1
Choose one of the following:
1. Create DOS partition or Logical DOS Drive
2. Set active partition
3. Delete partition or Logical DOS Drive
4. Display partition information
Enter choice: [1]
Press Esc to exit FDISK
4. Press Enter to select the default
[1]. The following screen will be displayed:
Create DOS Partition or Logical DOS Drive
Current fixed disk drive: 1
Choose one of the following:
1. Create Primary DOS Partition
2. Create Extended DOS Partition
3. Create Logical DOS Drive(s) in the Extended DOS Partition
Enter choice: [1]
Press Esc to return to FDISK Options
5. Again, press Enter to select the
default. The following will be displayed
Create Primary DOS partition
Current fixed disk drive : 1
Verifying drive integrity, xx% complete.
Current fixed disk drive: 1
Do you wish to use the maximum available
size for a primary DOS partition
and make the partition active (Y/N) ....................? [Y]
At this point you can press the Enter
key and make the entire drive one partition, your C: drive, or enter
N and make a partition which occupies less than the entire drive. I
parted this drive into a 4 GB C: drive and allocated the rest of the
drive to the D: drive. The menus are quite self explanatory for
accomplishing this task. You will also want to create an
Extended DOS partition and assign logical drive D: to it (fdisk should
do that automatically after the partition is created). You must
exit fdisk and reboot after creating each partition. Only one of
the partitions can be active. The active partition is the one which
will boot after Windows is installed. Make sure the primary partition
is Active by displaying the partition information.
HIGH-LEVEL FORMATTING. Once the
hard disk is partitioned and a partition is made active, the partitions
must be high-level formatted for the operating system that will use them. The
Windows FORMAT.COM is used to accomplish this process. A high-level
format further defines the the partition on a hard disk.
After creating the partitions and making sure
the primary DOS partition is active, reboot the computer to the Startup Floppy
or CD-ROM, select Start Computer with CD-ROM support, and format
the C: drive as follows:
Startup Floppy... A:\> format
c:
CD-ROM...
A:\> d:
D:\> cd win98
D:\> format c:
Do not use the /s flag with the format
command. We do not want to transfer the system files from the floppy
to the hard disk. Windows 98 will not install on the hard disk
if it already has the system files on it.
Get a cup of coffee...
6. Repeat for the D: drive. Get
two cups of coffee.
We can install Windows 98 from the CD or we
can copy the requisite files to the hard disk and install it from the hard
disk. The first method saves about 110 MBytes of hard disk space. The
second has the advantage that the CD is not required every time windows needs
a driver, etc. such as when changing the network configuration.
7. First method. To install
using the first method, boot to the Startup Floppy or Windows CD as described
in Part 7. With the CD you can simply select the first choice in the
second menu, but that is not the way I do it because part of that process
is to make a Startup floppy which takes time. So, select "2. Start
computer with CD-ROM support" from the menu to get to the DOS prompt.
8. Since we formatted two partitions
on the hard disk in Part 7, the CD-ROM should now be drive E: Change
the current drive to drive E:, change directory to \win98, and start the
Windows Setup as follows:
A:\> e:
E:\> cd \win98
E:\win98> setup /ie
The ie flag tells setup not to make a
Startup floppy. Don;t run setup from E:\
9. Second method. To install
using the second method and to use a convention that is in common practice,
make a windows\options\cabs directory on the hard disk, copy the files in
the e:\win98 directory to it, and run setup from the hard disk as follows:
A:\> c:
C:\> md windows
C:\> cd windows
You can type cd and use the F3 key
to repeat the rest of make directory command to speed up changing to
a directory you just created.
C:\WINDOWS> md options
C:\WINDOWS> cd options
C:\WINDOWS\OPTIONS > md cabs
C:\WINDOWS\OPTIONS > cd cabs
C:\WINDOWS\OPTIONS\CABS > copy e:\win98\*.*
This copies a bunch of cab files, etc.
to the hard disk.
C:\WINDOWS\OPTIONS\CABS > setup /ie
You may want to be non-conventional and
move the cab files to the D: drive which has a lot of space; e.g., D:\win98cab.
10. After setup runs scandisk you can
simply Exit scandisk. I wouldn't bother doing a surface scan at this
point; it would take a very long time.
11. Shortly thereafter, with this method,
setup will discover there is already a windows directory and suggest installing
windows in another directory: c:\windows.000. Do not let it install
windows in the c:\windows.000 directory; you want it in the c:\windows directory. Choose
select another directory, Backspace four times to remove ".000" and
ignore the setup warning about overwriting stuff in the Windows directory--it
won't in this case.
12. Complete the Windows installation
selecting setup defaults and following setup instructions. I won't
elaborate. The process is simple, straight forward, and requires no
cookbook instructions. Unless something is defective, you should not
encounter any Windows setup problems with this motherboard and the other
items in the bill of materials.
13. After Windows is installed and the
computer has rebooted for the last time, insert the CD which came with the
motherboard. Wait until the menu is displayed and install the AM
K7 INF update.
14. This install will erroneously leave
an unclosed DOS window. Hold the Ctrl and Alt keys and
press the Delete key to display the Windows Close Program window and
click the End Task button to close DOS window. This will also
reboot Windows.
15. After the reboot, Windows will install
several drivers. Just click the Next button through the process
and then click Yes when it prompts for a reboot.
16. If you were booting to the Windows
CD instead of a Startup floppy, reboot the computer, press the Delete key
to get into the CMOS Setup, select Advance BIOS Features, press the Enter
Key, Select First Boot device, use the Page Up/Down keys to Select Floppy
(or HDD-0), Esc to the Main Menu, select Save & Exit Setup.
Notes:
1. The analogy of the hard disk heads
flying like airplane is quite correct. The heads are moving relative
to the platter if the observer is on the platter. The behavior is similar
to a model airplane in a wind tunnel. The aerodynamics are the same.
2. From history reference "First
disk drive to use low-mass heads, lubricated disks, and sealed assembly,
which came to be known as Winchester drive technology and set the industry
standard for the next decade. The 3340 Winchester drive featured two spindles
with a storage capacity of 30 million characters each, hence 30-30, or 'Winchester.'"
3. From Seagate This
is called STIR (seek to improve reliability). This is designed to prevent
the heads from remaining in any given position for extended periods of
time. Since the heads are flying a very short distance above the media,
and are flying on a cushion of air, the compression of the air beneath
the head does impart a small amount of heat to the media because of the
friction involved. If the heads remained over a cylinder for extended periods
of time, the heat build-up on the media in a small localized area could
degrade the media in that particular locality. So, periodically during
idle, the heads will be moved to another cylinder and the servo recalibrated
for all heads. This is perfectly normal.
Larry
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References
Technical
Committee T13 AT Attachment
1. Upgrading and Repairing PCs, Sixth Edition, Scott
Mueller, Que (Believe it is in the tenth edition now; more detail than
presented here)
Interesting
stuff about boot sectors.
The
Enhanced IDE/Fast-ATA FAQ
The
Anatomy of Hard Disk Design by Albert Dayes (detailed stuff,
but interesting)
Whys
and wherefores of formatting hard drives by Brian K. Lewis (short
and well-written)
Basic
Description of Banded Sector Servo IBM
No-ID
sector format IBM
The
era of giant magnetoresistive heads by Jim Belleson, IBM Storage
Systems Division, & Ed Grochowski, IBM Almaden Research Center
A
history of IBM "firsts" in storage technology
Ultra
ATA/66 Extends Existing Technology While Increasing Performance and Data
Integrity Western Digital
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