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A kilobyte (kB) is 1000 bytes.
A megabyte (MB) is 1000 kB.
A gigabyte (GB) is 1000 MB.
A terabyte (TB) is 1000 GB.
This is the
SI norm.
However, there are people that use 1 MB=1024000 bytes and talk
about 1.44 MB floppies, and people who think that 1 MB=1048576 bytes.
Here I follow the
recent standard
and write Ki, Mi, Gi, Ti for the binary units, so that
these floppies are 1440 KiB (1.47 MB, 1.41 MiB),
1 MiB is 1048576 bytes (1.05 MB),
1 GiB is 1073741824 bytes (1.07 GB)
and 1 TiB is 1099511627776 bytes (1.1 TB).
Quite correctly, the disk drive manufacturers follow the SI norm
and use the decimal units. However, Linux kernel boot messages
(for not-so-recent kernels) and some old fdisk-type programs
use the symbols MB and GB for binary, or
mixed binary-decimal units. So, before you think your disk is
smaller than was promised when you bought it, compute first the
actual size in decimal units (or just in bytes).
Concerning terminology and abbreviation for binary units,
Knuth
has an alternative
proposal, namely
to use KKB, MMB, GGB, TTB, PPB, EEB, ZZB, YYB and to call these
large kilobyte, large megabyte, ... large yottabyte.
He writes: `Notice that doubling the letter connotes both
binary-ness and large-ness.' This is a good proposal -
`large gigabyte' sounds better than `gibibyte'. For our purposes
however the only important thing is to stress that a megabyte
has precisely 1000000 bytes, and that some other term and abbreviation
is required if you mean something else.
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