Hard Disk Technology

Hard disk technology is the preferred type of main storage for most computer systems. A hard disk is one or more platters and their associated read-write heads. A hard disk platter is a flat, rigid disk made of aluminum or glass and coated with magnetic iron oxide particles. Hard disk platters are sealed inside the drive case or cartridge to screen out dust and other contaminants. The sealed case contains disk platters and read-write heads. Each platter has a read-write head that hovers over the surface to read data. The drive spindle supports one or more hard disk platters. Both sides of the platter are used for data storage. More platters mean more data storage capacity. Hard disk platters rotate as a unit on the spindle to position read-write heads over specific data. The platters spin continuously, making thousands of rotations per minute. Each data storage surface has its own read-write head, which moves in and out from the center of the disk to locate data. The head hovers only a few microinches above the disk surface, so the magnetic field is more compact than on a floppy disk. As a result, more data is packed into a smaller area on a hard disk platter. The density of particles on the disk surface provides hard disks with capacities far greater than floppy disks. Also, the access time for a hard disk is significantly faster than for a floppy disk.

A hard disk drive stores data at the same locations on all platters before moving the read-write heads to the next location. A vertical stack of storage locations is called a “cylinder” – the basic storage bin for a hard disk drive. A hard drive mechanism includes a circuit board called a controller that positions the disk and read-write heads to locate data. The storage technology used on many PCs transfers data from a disk, through the controller, to the processor, and finally to RAM before it is actually processed.

Hard disks are not as durable as many other storage technologies. The read-write heads in a hard disk hover a microscopic distance above the disk surface. If a read-write head runs into a dust particle or some other contaminant on the disk, it might cause a head crash, which damages some of the data on the disk. To help prevent contaminants from contacting the platters and causing head crashes, a hard disk is sealed in its case. A head crash can also be triggered by jarring the hard disk while it is in use. Although hard disks have become considerably more rugged in recent years, you should still handle and transport them with care. You should make a backup copy of the data stored on your hard disk in case of a head crash.

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