Hard Drives- How They Work

The logic board is the board of chips underneath the drive. It controls the spindle and head actuator and also translates data to a form usable by the controller and the rest of the system. Some logic boards have an integrated controller, also. Sometimes, an apparent disk failure is actually a failure of the logic board. In such a case, you can replace the logic board and regain access to the data held up on the drive. This is relatively easy to do, because the board is simply plugged into the drive and held in by screws.

Data Storage

I have discussed the structure of a platter itself, but how exact is data stored on that? First, the heads are actually small electromagnets. To write information to the platter, a small electrical current is pulsed from the electronics of the drive to the head. The direction of the current, and thus the direction of the magnetic field between the head and the platter, determine whether or not the data bit is a 1 or a 0 in binary (which is the only language a PC understands). This magnetic field alters the direction of the little magnets on that portion of the platter. The “little magnets” are actually microscopic, the size of a molecule. The direction of the magnet is retained over time and remains that way unless rewritten to reflect something different. Thus, the hard drive will retain this data even after it is powered off.

Capacity

Just take a trip to the computer store and you can see that there have been major advancements in hard drive technology that lead to larger capacity drives. Where there were once 500MB drives, we now have huge drives. Recently, a 36GB IDE drive was released. What led to this?

Well, the first thought would be: Add more platters, or maybe bigger ones. Well, yeah, larger platters would do the trick. 5.25″ platters have been used on older drives, and do hold more data. But, manufacturers don’t use these big platters because of the extra stresses the larger platters put on the motor. These stresses, and the simple fact that the heads have more disk to cover, make the drives hotter and a lot bigger. Most drives in use today use 3.5″ platters, and 2.5″ or smaller is commonly used for notebook systems. So, the manufacturer decides it would be better to keep smaller platters, but just add more of them. This works, but in order to reach such high capacities, you’d need a lot of platters. The vertical heights of these drives would just be too much. So, then what?

Keyword: Areal Density. This is the closeness of data bits on the hard disk to each other, usually measured in megabytes per square inch (MBSI). There are a few factor that go into determining the degree of areal density that is possible:

• Size of the magnetic particles in the platter itself


• Size of the read/write heads. Smaller heads allow larger densities.


• “Altitude” of the heads over the platter surface.

This density increases performance and allows more data to be packed onto a platter. The closeness of the bits together mean that more data passes the head at a time, increasing read/write performance. By combining this with increase platter rotation speeds, latencies will be lower and speed will be higher.

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