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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