SIZE MEASUREMENT CONVENTIONS

5/4/97

Size Measurement Conventions: As with distances, weights and other measurements that can cover a wide range of magnitudes, it is convenient to report sizing of computer usage in units that break at factors of a thousand or so. Thus, capacities are often reported in bytes, kilobytes, (1000 bytes). Megabytes (1,000,000) bytes, Gigabytes (1,000,000,000) and soon Terabytes (1,000,000,000,000 bytes). However, computer hardware and software is almost always simpler when working with units that are powers of 2. For several decades, the convention in all phases of computing has been to use 2 to the 10th power -- 1024 -- as the basic unit of sizing. The abbreviations commonly used are:

All well and good until the marketing people came along.

Take a disk drive capable of storing 536,870,912 bytes. One could list this as being a 512Mb (536,870,912/1,048,576) Drive. But your competitor is likely to divide by 1,000,000 rather than 1,048,576 and sell their drive as a 536Mb. Same drive, but it looks 5% bigger.

Worse, should this drive grow by a factor of 1024, some engineers will divide the size (512mb or 536mb) by 1000 in scaling the new value whereas others will divide by 1024. As reported sizes grow it becomes less and less certain what they actually represent.

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