General Science, Mathematics, and Technology


Why does the actual amount of computer storage space differ from the advertised amount of storage?

Computer storage space for hard drives and other storage media is calculated in base 2 using binary format with a byte as the basic unit. The common units of computer storage are:

Kilobyte (KB)    1,024 bytes

Megabyte (MB)    1,024 kilobytes or 1,048,576 bytes

Gigabyte (GB)    1,024 megabytes or 1,073,741,824 bytes

Terebyte (TB)    1,024 gigabytes or 1,099,511,627,776 bytes

However, since consumers are more familiar with the decimal, base 10, system of numbers, computer manufacturers describe storage sizes in base 10 where one megabyte is one million bytes and one gigabyte is one billion bytes. Therefore, for each gigabyte they are over reporting storage space by 73,741,824 bytes. The concept is further complicated because some storage media may have the actual amount of advertised storage, but some of the available storage is lost due to formatting.


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