67 lines
2.5 KiB
HTML
67 lines
2.5 KiB
HTML
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<TITLE>Large Disk HOWTO: Units</TITLE>
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<H2><A NAME="units"></A> <A NAME="s2">2. Units</A></H2>
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<P>
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<!--
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units!megabyte
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-->
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<!--
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units!gigabyte
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-->
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A kilobyte (kB) is 1000 bytes.
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A megabyte (MB) is 1000 kB.
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A gigabyte (GB) is 1000 MB.
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A terabyte (TB) is 1000 GB.
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This is the
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<A HREF="http://physics.nist.gov/cuu/Units/prefixes.html">SI norm</A>.
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However, there are people that use 1 MB=1024000 bytes and talk
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about 1.44 MB floppies, and people who think that 1 MB=1048576 bytes.
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Here I follow the
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<A HREF="http://physics.nist.gov/cuu/Units/binary.html">recent standard</A>
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and write Ki, Mi, Gi, Ti for the binary units, so that
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these floppies are 1440 KiB (1.47 MB, 1.41 MiB),
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1 MiB is 1048576 bytes (1.05 MB),
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1 GiB is 1073741824 bytes (1.07 GB)
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and 1 TiB is 1099511627776 bytes (1.1 TB).
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<P>Quite correctly, the disk drive manufacturers follow the SI norm
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and use the decimal units. However, Linux kernel boot messages
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(for not-so-recent kernels) and some old fdisk-type programs
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use the symbols MB and GB for binary, or
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mixed binary-decimal units. So, before you think your disk is
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smaller than was promised when you bought it, compute first the
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actual size in decimal units (or just in bytes).
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<P>Concerning terminology and abbreviation for binary units,
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<A HREF="http://www-cs-staff.stanford.edu/~knuth/">Knuth</A>
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has an alternative
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<A HREF="http://www-cs-staff.stanford.edu/~knuth/news99.html">proposal</A>, namely
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to use KKB, MMB, GGB, TTB, PPB, EEB, ZZB, YYB and to call these
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<I>large kilobyte</I>, <I>large megabyte</I>, ... <I>large yottabyte</I>.
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He writes: `Notice that doubling the letter connotes both
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binary-ness and large-ness.' This is a good proposal -
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`large gigabyte' sounds better than `gibibyte'. For our purposes
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however the only important thing is to stress that a megabyte
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has precisely 1000000 bytes, and that some other term and abbreviation
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is required if you mean something else.
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<P>
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