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The Hard Drive

The main permanent storage device is the computer's hard drive (sometimes called a fixed disk), which can be either internal (mounted inside the computer case) or external (in its own case connected to the computer via a cable). A hard drive is actually a stack of disks coated with a magnetic coating similar to audioor videotape. Information is saved on a hard drive much the same way a song is recorded on audiotape. The computer's electronic signals are recorded on the magnetic hard drive disk, and when you want the information back, the hard drive "plays back" those signals. Saving information on a hard drive is called writing to the drive; playing information back is called reading. It is also possible to erase information on a drive; this is called deleting.

Disk storage capacity is measured in units called bytes. A byte is made up of 8 bits of information. A thousand bytes is a kilobyte, or K for short. A megabyte is 1024 K. One thousand megabytes is a gigabyte. Hard drives can store billions of bytes. Typically, hard drives store anywhere from 20 gigabytes—often called "gigs"—to several hundred gigabytes.


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