Definition of a Hard Disk

To many users, the hard disk drive is the most important and yet the most mysterious part of a computer system. A hard disk drive is a sealed unit that a PC uses for nonvolatile data storage. Nonvolatile, or semi-permanent, storage means that the storage device retains the data even when no power is supplied to the computer. Because the hard disk drive is expected to retain data until deliberately erased or overwritten, the hard drive is used to store crucial programming and data. As a result, when the hard disk fails, the consequences are usually very serious. To maintain, service, and upgrade a PC system properly, you must understand how the hard disk functions.

A hard disk drive contains rigid, disk-shaped platters, usually constructed of aluminum or glass. Unlike floppy disks, the platters cannot bend or flex—hence the term hard disk. In most hard disk drives, you cannot remove the platters, which is why they are sometimes called fixed disk drives. Removable hard disk drives are also available. Sometimes this term refers to a device in which the entire drive unit (that is, the disk and the drive) is removable, but it is more commonly used to refer to cartridge drives, where the platters are contained in a removable cartridge.

Hard Disk Features

To make the best decision in purchasing a hard disk for your system or to understand what distinguishes one brand of hard disk from another, you must consider many features. This section examines some of the issues you should consider when you evaluate drives:

• Capacity
• Reliability
• Performance
• Cost

HDD Manufactures

Seagate, Fujitsu, Hewlett-Packard, Maxtor, Samsung, Quantum and Western Digital.