The Computer Destruction Lab
Hard Drive Dissection
This is a Western Digital "Caviar" brand IDE hard drive. It is from
my computer after a head crash (more on how that happens later).
Worry not, no data was lost! In fact, this page is the gain.
This is the hard drive, upside down.
Older types of hard drives didn't have so much circuitry on the
drive itself, so the motherboard had to have a controller card
installed in order to use a hard disk. IDE hard drives, however,
have much of the controlling on the drive itself, making the
interface to the rest of the computer easier and making the
disk more flexible (figuratively). One of the things you can do
with on-drive controllers is remap bad sectors to extra cylinders
so the disk seems to the computer as if there are no bad sectors.
The top of the drive encasement
The most important information on this sticker is dritectly under
the line "AT Compatible Intelligent Drive." That next line
tells how many cylinders and heads the drive has. This was very
important up until a few years ago, when you had to tell the computer's
BIOS (Basic Input Output System) these parameters by hand. Modern
drives and BIOSes can talk directly — another result of the
on-drive controller card. The snide remark is something I wrote
on the drive after it failed; a quote from "Spaced Invaders."
The connectors
This is the "inside" end of the drive. On the left, a 40-pin IDE connector
(pin 1 toward the center). Next in line is the drive configuration.
"C" stands for Cable Select (rarely used), "S" is for Slave, the secondary
drive on a cable, and "M" is for master, the primary drive on a cable.
IDE specifications allow 2 drives on each cable, one Slave and one
Master. Finally, there is the connection to the Power Supply.
Circuits removed
The foam keeps the metal encasement from shorting the circuitry. In the middle
of the encasement is the motor that spins the disk, with 4 copper contacts.
In the lower left is a black receptor for the pins on the controller card.
Controller Card
You can see the motherboard connectors at the top. Less than halfway
down are the copper connectors that go to the motor. At the bottom
right is the pins that go into the drives data reading and writing
mechanism.
The case cracked open
The 3 discs layered are the "platters" of the hard drive. It's a magneticly
active metal, and is solid (hence the "hard" in hard disk, as opposed to
"floppy" disks). The motor spindle goes through the middle of the platters.
Below and to the right is where the pin connector makes contact, and a ribbon
cable connects the pins to the "heads" on the left. Think of them as a record
player's needle, if you're old enough.
If you look on the right side of the above picture, you'll see an air filter on
the far right. This air filter is very dirty!
The sealed inside of a hard drive has to be perfectly clean, so they are
essentially sealed. However, in the interest of keeping the drive cool,
there is an amount of air circulation inside.
The heads
Note that there are 6 heads, one for each side of the 3 platters. This is in spite of
the fact that the drive reports 16 heads to the motherboard. Old motherboards could
only handle a certain number of cylinders, and this drive has more. So the addressing
is abstracted by the controller to emulate 16 heads with 5 of the 6. The sixth one
is used as a map of the cylinders so the heads know when they've made contact with the
proper cylinder.
The platters
The data is actually stored on these layered platters. The space between them is
for the heads. Bits are stored magnetically, and the heads are read-write. In
general, an entire cluster is written at one time.
The motor
This is what's called a "Stepper Motor." Because of its design, the motor spins
at a very exact speed.
The casing
Sturdy contruction stabilizes the unit from vibrations. The motor, removed, at right.
A platter
An up-close of one of the platters, heads sandwiching it as they would in operation.
This ends the tour. Email me with comments or corrections.
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