Wednesday, October 10, 2012

What is a Hard Disk Drive

The hard disk drive (HDD) is one of the most important and yet mysterious parts of a computer system. HDDs are sealed units used for nonvolatile data storage. Nonvolatile, or semipermanent, storage means that the storage device retains the data even when no power is supplied to the computer. Because HDDs store crucial programming and data, the consequences of any failures are usually very serious.

Hard disk drives contain rigid, disk-shaped platters, usually constructed of aluminum or glass Unlike floppy disks, the platters can’t bend or flex—hence the term hard disk. In most drives you can’t remove the platters, which is why they are sometimes called fixed disk drives. Removable hard disk drives are also available.

Obviously, the large storage capacities found on modern drives are useless unless you can also quickly transfer the data to and from the disk. The hard disk as found in the original IBM XT in 1983 had a constant data transfer rate from the media of about 100KBps. Today, most commonly used drives feature average transfer rates of 100MBps or more, an increase of over 1,000 times. Much like the increase in drive capacity, the speed of the interface has also come a long way since the MFM and RLL interfaces that were commonplace in the ’80s. As always, the interfaces are much faster than the actual drives. Modern interfaces offer data transfer rates of up to 133MBps for Parallel ATA, 150MBps and 300MBps for Serial ATA, 320MBps bandwidth for Ultra-320 SCSI, and 300MBps or 600MBps for SAS. All these interfaces are much faster than the drives they support, meaning that the true transfer rate you will see is almost entirely limited by the drive and not the interface you choose. The modern interfaces have bandwidth to spare for future developments and advances in hard disk technology.

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