Adam M. Costello : Soap Box

Units of Information

Units of information, like “megabyte” or “Mb”, are often used inconsistently. It would be helpful to agree on some standard usage. Below is an old proposal of mine that tried, as much as possible, to be unambiguous, useful, and compatible with existing practice. The result was not particularly satisfying. I'm now inclined to think that there is no solution better than using expressions like 2^20 and 10^6 when precision is needed.

There is, however, an international standard, though I haven't heard of anyone using it. It specifies that the traditional prefixes, like kilo, mega, giga, always mean powers of ten; for powers of two the second syllable is replaced with “bi”, yielding kibi, mebi, gibi, etc. The abbreviated forms are Ki, Mi, Gi, etc. (simply append “i”, except k becomes Ki not ki).

Markus Kuhn wrote another proposal designed to be compatible with the SI units.

My old proposal follows.

  meaning    abbr.  pronunciation

              bit          bit
 2^10 bits   kbit      kilobit
 2^20 bits   Mbit      megabit
 2^30 bits   Gbit      gigabit
 2^40 bits   Tbit      terabit
 2^50 bits   Pbit      petabit
 2^60 bits   Ebit       exabit
 2^70 bits   Zbit     zettabit
 2^80 bits   Ybit     yottabit

    8 bits    byte         byte
 2^10 bytes  kbyte     kilobyte
 2^10 bytes  K or kB   kay or kilobyte
 2^20 bytes  Mbyte     megabyte
 2^30 bytes  Gbyte     gigabyte
 2^40 bytes  Tbyte     terabyte
 2^50 bytes  Pbyte     petabyte
 2^60 bytes  Ebyte      exabyte
 2^70 bytes  Zbyte    zettabyte
 2^80 bytes  Ybyte    yottabyte
10^6  bytes  M or MB    meg
10^9  bytes  G or GB    gig (hard g, not like jig)
10^12 bytes  T or TB    ter (pronounced like tear)
10^15 bytes  P or PB    pet
10^18 bytes  E or EB     ex
10^21 bytes  Z or ZB    zet
10^24 bytes  Y or YB    yot

      bit/s   bps          bit(s)-per-second or       bee-pee-ess
10^3  bit/s  kbps     kilo-bit(s)-per-second or  kilo-bee-pee-ess
10^6  bit/s  Mbps     mega-bit(s)-per-second or  mega-bee-pee-ess
10^9  bit/s  Gbps     giga-bit(s)-per-second or  giga-bee-pee-ess
10^12 bit/s  Tbps     tera-bit(s)-per-second or  tera-bee-pee-ess
10^15 bit/s  Pbps     peta-bit(s)-per-second or  peta-bee-pee-ess
10^18 bit/s  Ebps      exa-bit(s)-per-second or   exa-bee-pee-ess
10^21 bit/s  Zbps    zetta-bit(s)-per-second or zetta-bee-pee-ess
10^24 bit/s  Ybps    yotta-bit(s)-per-second or yotta-bee-pee-ess

Appending /s (pronounced “per second”) to any byte unit abbreviation is straightforward and unambiguous. Appending /s to a bit unit is unambiguous when written (a Mbit/s is a megabit per second, not a mega(bit-per-second)), but there is no unambiguous pronunciation, because of the bps units. Luckily, in practice data rates using bit units are almost always in powers of 10.


[AMC]  Prepared by Adam M. Costello
 Last modified: 2001-Oct-14-Sun 03:40:36 GMT
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