units

Section: Environments, Tables, and Troff Macros (7)
Updated: 2023-02-10
Index Return to Main Contents
 

NAME

units - decimal and binary prefixes  

DESCRIPTION

 

Decimal prefixes

The SI system of units uses prefixes that indicate powers of ten. A kilometer is 1000 meter, and a megawatt is 1000000 watt. Below the standard prefixes.
PrefixNameValue
qquecto10ha-30 = 0.000000000000000000000000000001
rronto10ha-27 = 0.000000000000000000000000001
yyocto10ha-24 = 0.000000000000000000000001
zzepto10ha-21 = 0.000000000000000000001
aatto10ha-18 = 0.000000000000000001
ffemto10ha-15 = 0.000000000000001
ppico10ha-12 = 0.000000000001
nnano10ha-9 = 0.000000001
µmicro10ha-6 = 0.000001
mmilli10ha-3 = 0.001
ccenti10ha-2 = 0.01
ddeci10ha-1 = 0.1
dadeka10ha 1 = 10
hhecto10ha 2 = 100
kkilo10ha 3 = 1000
Mmega10ha 6 = 1000000
Ggiga10ha 9 = 1000000000
Ttera10ha12 = 1000000000000
Ppeta10ha15 = 1000000000000000
Eexa10ha18 = 1000000000000000000
Zzetta10ha21 = 1000000000000000000000
Yyotta10ha24 = 1000000000000000000000000
Rronna10ha27 = 1000000000000000000000000000
Qquetta10ha30 = 1000000000000000000000000000000

The symbol for micro is the Greek letter mu, often written u in an ASCII context where this Greek letter is not available.  

Binary prefixes

The binary prefixes resemble the decimal ones, but have an additional 'i' (and "Ki" starts with a capital 'K'). The names are formed by taking the first syllable of the names of the decimal prefix with roughly the same size, followed by "bi" for "binary".
PrefixNameValue
Kikibi2ha10 = 1024
Mimebi2ha20 = 1048576
Gigibi2ha30 = 1073741824
Titebi2ha40 = 1099511627776
Pipebi2ha50 = 1125899906842624
Eiexbi2ha60 = 1152921504606846976
Zizebi2ha70 = 1180591620717411303424
Yiyobi2ha80 = 1208925819614629174706176
 

Discussion

Before these binary prefixes were introduced, it was fairly common to use k=1000 and K=1024, just like b=bit, B=byte. Unfortunately, the M is capital already, and cannot be capitalized to indicate binary-ness.

At first that didn't matter too much, since memory modules and disks came in sizes that were powers of two, so everyone knew that in such contexts "kilobyte" and "megabyte" meant 1024 and 1048576 bytes, respectively. What originally was a sloppy use of the prefixes "kilo" and "mega" started to become regarded as the "real true meaning" when computers were involved. But then disk technology changed, and disk sizes became arbitrary numbers. After a period of uncertainty all disk manufacturers settled on the standard, namely k=1000, M=1000 k, G=1000 M.

The situation was messy: in the 14k4 modems, k=1000; in the 1.44 MB diskettes, M=1024000; and so on. In 1998 the IEC approved the standard that defines the binary prefixes given above, enabling people to be precise and unambiguous.

Thus, today, MB = 1000000 B and MiB = 1048576 B.

In the free software world programs are slowly being changed to conform. When the Linux kernel boots and says

hda: 120064896 sectors (61473 MB) w/2048KiB Cache

the MB are megabytes and the KiB are kibibytes.  

SEE ALSO

The International System of Units


 

Index

NAME
DESCRIPTION
Decimal prefixes
Binary prefixes
Discussion
SEE ALSO

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Time: 19:12:09 GMT, March 28, 2024