Binary measurements and units of measure. See also Binary Numbers.

Units

In computers, information is stored electronically as the binary digits 0 and 1, also referred to as 'off' and 'on' respectively.

Beware that people get their bs and Bs mixed up! Except for shysters, most people should try to be consistent with using bits (b) when discussing rates and bytes (B) when discussing storage. Sometimes what is expressed in bits, actually refers to bpp (bits per pixel).

Since bits and bytes are binary, their multiples are also  expressed in binary powers: 2^10, 2^30, 2^40, 2^50, 2^60. While almost everyone is consistent about meaning binary powers for bits, there is a lot of inconsistency when it comes to bytes.

My solution would remove all ambiguity by using the IEC system but also add new prefixes for decimal powers. EG: "MiB" for binary and "MeB" for decimal! I think it's a brilliant idea that I came up with today [2004-07-31].

Multiple Prefix Metric Symbol GH   Multiple Name Prefix Symbol
1e24 yotta Y Ye   280 ~ 1.21e24 yottabinary  Yobi Yi 
1e21 zetta Z Ze   270 ~ 1.18e21 zettabinary  Zebi Zi
1e18 exa E Ee   260 ~ 1.15e18 exabinary exbi Ei
1e15 peta P Pe   250 ~ 1.13e15 petabinary pebi Pi
1e12 tera T Te   240 ~ 1.10e12 terabinary tebi Ti
1e09 giga G Ge   230 ~ 1.07e09 gigabinary gibi Gi
1e06 mega M Me   220 ~ 1.05e06 megabinary mebi Mi
1e03 kilo k --> K Ke   210 ~ 1.02e03 = 1024 kilobinary kibi Ki

Since this is my site, it shall be the law on this site henceforth. --> 2005-04-20: No way! My system was too annoying. Henceforth, my site will use SI prefixes (K, M, G, T, P, etc.) for binary units but the multiple will be binary powers instead of decimal. EG: When I say "4 MB", I mean "4 * 2^20 bytes" instead of "4e6 bytes".

For reference, here are common powers of 2:

Power Decimal Decimal
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
...
31
32
..
63
64
...
127
128
1.00e+0
2.00e+0
4.00e+0
8.00e+0
1.60e+1
3.20e+1
6.40e+1
1.28e+2
2.56e+2
5.12e+2
1.02e+3
2.04e+3
4.09e+3
8.19e+3
1.63e+4
3.27e+4
6.55e+4
1.31e+5
2.62e+5
5.24e+5
1.04e+6
...
2.14e+9
4.29e+9
...
9.22e+18
1.84e+19
...
1.70e+38
3.40e+38
1
2
4
8
16
32
64
128
256
512
1,024
2,048
4,096
8,192
16,384
32,768
65,536
131,072
262,144
524,288
1,048,576
...
2,147,483,648
4,294,967,296
...
9,223,372,036,854,775,808
18,446,744,073,709,551,616
...

Common Sizes

Common Rates

Rates are also commonly expressed in bits per second (bps or b/s), kbps (Kb/s), Mbps (Mb/s), and Gbps (Gb/s). Note that it is in BITS not BYTES.

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