White Paper

ISS Technology Update Volume 9, Number 1

edition, Letter symbols to be used in electrical technology – Part 2: Telecommunications and electronics. Table 1-2 lists the

names and symbols for the adopted binary prefixes. Pronounce the first two letters in each symbol like the corresponding SI unit

followed by "bi" (short for binary, but pronounced "bee"). For example, one kibibyte (pronounced ki-bee-byte) is written as

1 KiB = 2

B = 1024 B.

Table 1-2. Binary prefixes adopted by the IEC

Factor Value Name Symbol

1,024

kibi Ki

1,048,576

mebi Mi

1,073,741,824

gibi Gi

1,099,511,627,776

tebi Ti

1,125,899,906,842,624

pebi Pi

1,152,921,504,606,846,976

exbi Ei

1,180,591,620,717,411,303,424

zebi Zi

1,208,925,819,614,629,174,706,176

yobi Yi

Reducing the confusion

To reduce confusion, vendors are pursuing one of two remedies: they are changing SI prefixes to the new binary prefixes, or

they are recalculating the numbers as powers of ten.

For disk and file capacities, the latter remedy is more popular because it is much easier to recognize that 300 GB is the same

as 300,000 MB than to recognize that 279.4 GiB is the same as 286,102 MiB. For example, in 2009, the SourceForge web

site reported file sizes using binary prefixes for several months before changing back to SI prefixes but switching the file sizes to

powers of ten.

For memory capacities, binary prefixes are more natural. For example, reporting a Smart Array controller cache size of

512 MiB is preferable to reporting it as 536.9 MB.

HP is considering modifying its storage utilities to report disk capacity with correct decimal and binary values side-by-side (for

example, "300 GB (279.4 GiB)"), and report cache sizes with binary prefixes ("1 GiB"). Let us know what you think. Provide

your comments to the HP Reality Check: Server Insights blog at http://www.communities.hp.com/online/blogs/reality-check-

server-insights/default.aspx.

Additional resources

For additional information on the topics discussed in this article, visit the following sites:

Resource URL

SI prefixes

http://www.bipm.org/en/si/si_brochure/chapter3/prefixes.html

IEC article : Prefixes for binary multiples

http://www.iec.ch/zone/si/si_bytes.htm

Binary prefixes

http://en.wikipedia.org/wiki/Binary_prefix

Reprinted with permission of the IEC (see Legal Notices).