Bytes, kilobytes, megabytes, and gigabytes

Chapter Bytes, kilobytes, megabytes, and gigabytes

Teach Yourself Electricity and Electronics Third Edition Book
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Teach Yourself Electricity and Electronics Third Edition Book

  • Bytes, kilobytes, megabytes, and gigabytesA byte is a unit of digital data, consisting of a string of eight bits. One byte constitutesroughly the same amount of data as one character, such as a letter, numeral, punc-tuation mark, space, or line-feed/return command.Today’s computers work with files that are very large in terms of bytes. Therefore,kilobytes (units of 2101024 bytes), megabytes (units of 2201,048,576 bytes), andgigabytes (units of 2301,073,741,824 bytes) are commonly mentioned by people talk-ing about computers. The abbreviations for these units are KB, MB, and GB, respec-tively. Alternatively you might see them abbreviated as K, M, and G.As computer technology advances during the new century, you’ll be hearing moreand more about a unit of data called a terabyte (TB or T). This is equivalent to 240 bytes,or 1,048,576 MB. And the day might come when we commonly use the terms petabyte(PB or P), which refers to 250 bytes or 1,048,576 GB, and even exabyte (EB or E), whichrefers to 260 bytes of 1,048,576 TB. Does that sound incredible? If so, think about thefact that even a computer with storage or memory capacities in the exabyte range can-not begin to approach the sophistication and subtlety of the human mind. But never-theless, a machine juggling a few exabytes of data might have a fascinating, if perhapsalien, sort of intelligence.Personal-computer memory is usually specified in megabytes or gigabytes. Thesame holds true for removable data storage media such as diskettes. The hard drive ina computer generally has capacity measured in gigabytes, although a few get into theterabyte range. Older computers might have hard-drive capacities quoted as a few hun-dred megabytes or less.The hard driveA hard drive, also known as a hard disk, is a common form of mass storage for com-puter data. The drive consists of several disks, called platters, arranged in a stack.They are made from aluminum or other rigid material, coated with a ferromagneticsubstance similar to that used in audio or video tape. The platters are spaced a frac-tion of an inch apart. Each has two sides (top and bottom) and two read/writeheads (one for the top and one for the bottom). The assembly is enclosed in a sealedcabinet. Figure 33-2A is an edgewise, cutaway view of the platters and heads in atypical hard drive.Drive actionWhen the computer is switched off, the hard drive mechanism locks the heads in aposition away from the platters. This prevents damage to the heads and platters ifthe computer is moved. When the computer is powered up, the platters spin at sev-eral thousand revolutions per minute (rpm). The heads hover a few millionths of aninch above and below the platter surfaces.When you type a command or click on an icon telling the computer to read or writedata, the hard drive mechanism goes through a series of rapid, complex, and precisemovements. The head must be positioned over the particular spot on the platter where626 Computers and the Internet