Hard Drive Size Discrepancy

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Hard Drive Size Discrepancy

Note: If you're using Snow Leopard, disregard this section.

Why does my new 500 GB hard drive report it only has 465 GB? Have I been ripped off?

No, you haven't been ripped off. 500 GB = 465 GB, strange as it seems.

The reason is that computers count a "kilo" something as 1024 (binary 2^10) while the rest of the world count a "kilo" as 1000 (decimal 10^3). A 'mega' in computer binary system is 1024 x 1024 = 1,048,576 (rather than decimal 1,000,000), and a 'giga' is 1024 x 1024 x 1024 = 1,073,741,824 rather than decimal 1,000,000,000

This creates a discrepancy of approximately 7% between the number of GB the computer reports, and what is advertised as the drive's capacity in GB. It is important to note that there is no difference in the number of actual bytes of storage - it is only a difference in reporting when the binary 'giga' terminology is used.

A 500 GB hard drive has about 500,000,000,000 bytes (it is never exact, commonly a drive is designed to have more bytes, to allow for a certain number of defective sectors to be mapped out). When counted on the computer, 500 Gb (decimal) = 500 billion bytes = 465.66 GB (binary).

Some propose using a different term, gibibyte (GiB) for the binary figure, however that is unlikely to catch on in the marketplace.

More information is at