Kilo, Mega, Giga, and all that stuff…
Kilo, mega, giga, …
Kilo, mega, giga, tera, and peta are among the list of prefixes that are used to denote the quantity of something,
such as, in computing and telecommunications, a byte or a bit. Sometimes called prefix multipliers, these prefixes
are also used in electronics and physics. Each multiplier consists of a one-letter abbreviation and the prefix that it
stands for.
In communications, electronics, and physics, multipliers are defined in powers of 10 from 10-24 to 1024, proceeding
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in increments of three orders of magnitude (10 or 1,000). In IT and data storage, multipliers are defined in powers
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of 2 from 2 to 2 , proceeding in increments of ten orders of magnitude (210 or 1,024). These multipliers are
denoted in the following table.
Prefix
Symbol(s)
Power of 10
Power of 2
yocto-
y
10-24 *
--
zepto-
z
10-21 *
--
atto-
a
10-18 *
--
femto-
f
10-15 *
--
pico-
p
10-12 *
--
nano-
n
10-9 *
--
10-6 *
--
10-3 *
--
micromilli-
m
-2
--
d
-1
10 *
--
(none)
--
0
10
20
deka-
D
101 *
--
hecto-
h
102 *
--
kilo-
k or K **
103
210
mega-
M
106
220
giga-
G
109
230
tera-
T
1012
240
peta-
P
1015
250
exa-
E
1018 *
260
zetta-
Z
1021 *
270
yotta-
Y
1024 *
280
centideci-
c
10 *
* Not generally used to express data speed
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10
** k = 10 and K = 2
Examples of quantities or phenomena in which power-of-10 prefix multipliers apply include frequency (including
computer clock speeds), physical mass, power, energy, electrical voltage, and electrical current. Power-of-10
multipiers are also used to define binary data speeds. Thus, for example, 1 kbps (one kilobit per second) is equal
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to 10 , or 1,000, bps (bits per second); 1 Mbps (one megabit per second) is equal to 10 , or 1,000,000, bps. (The
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lowercase k is the technically correct symbol for kilo- when it represents 103, although the uppercase K is often
used instead.)
When binary data is stored in memory or fixed media such as a hard drive, diskette, ZIP disk, tape, or CD-ROM,
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power-of-2 multipliers are used. Technically, the uppercase K should be used for kilo- when it represents 2 .
10
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Therefore 1 KB (one kilobyte) is 2 , or 1,024, bytes; 1 MB (one megabyte) is 2 , or 1,048,576 bytes.
The choice of power-of-10 versus power-of-2 prefix multipliers can appear arbitrary. It helps to remember that in
common usage, multiples of bits are almost always expressed in powers of 10, while multiples of bytes are almost
always expressed in powers of 2. Rarely is data speed expressed in bytes per second, and rarely is data storage
or memory expressed in bits. Such usages are considered improper. Confusion is not likely, therefore, provided
one adheres strictly to the standard usages of the terms bit and byte.
Kibi, mebi, gibi, tebi, pebi, and all that
Kibi, mebi, gibi, tebi, pebi, and exbi are binary prefix multipliers that, in 1998, were approved as a standard by the
International Electrotechnical Commission (IEC) in an effort to eliminate the confusion that sometimes occurs
between decimal (power-of-10) and binary (power-of-2) numeration terms.
At present, the prefix multipliers kilo- (k or K), mega- (M), giga- (G), tera- (T), peta- (P), and exa- (E) are
ambiguous. In most of the physical sciences, and when describing quantities of objects generally, these
multipliers refer to powers of 10. However, when used to define data quantity in terms of bytes, they refer to
powers of 2. The following table denotes the most often-used prefixes and their meanings.
Prefix
Symbol(s)
Power of 10
Power of 2
kilo-
k or K **
103
210
mega-
M
106
220
giga-
G
109
230
tera-
T
1012
240
peta-
P
1015
250
exa-
E
1018 *
260
* Not generally used to express data speed
** k = 103 and K = 210
The power-of-10 multipliers and the power-of-2 multipliers for a given word prefix are almost, but not quite, the
same. For example, the power-of-10 definition of kilo- (k) refers to 1,000, while the power-of-2 definition (K) refers
to 1,024. As if this is not confusing enough, when referring to a data speed of one kilobit per second (1 kbps),
analysts generally mean 1,000 bits per second (103 bps), but when talking about one kilobyte (1 KB) of data
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storage, they usually mean 1,024 bytes (2 B). This prevailing confusion could be eliminated (some computer
scientists believe) by adopting special prefixes referring to the binary quantities. The proposed scheme is as
follows.
Full Technical
Name
Proposed
prefix
Proposed
symbol
Numeric
multiplier
kilobinary
kibi-
Ki
210
megabinary
mebi-
Mi
220
gigabinary
gibi-
Gi
230
terabinary
tebi-
Ti
240
petabinary
pebi-
Pi
250
exabinary
exbi-
Ei
260
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In scenarios such as the one mentioned above, if the new binary prefixes are used, it should be easy to know
whether an engineer is talking or writing about the decimal or binary multiplier. We will know that one kilobit per
second (1 kbps) means 1,000 bps, and one kibibyte (1 KiB) means 1,024 bytes, for example.
As of this writing, the binary prefix multipliers have not yet come into general use.
Pronunciation: Based on a suggestion from NIST, "the first syllable of the name of the binary-multiple prefix
should be pronounced in the same way as the first syllable of the name of the corresponding International
Standard (SI) prefix, and the second syllable should be pronounced as 'bee.'" Thus, "kibi" would be pronounced
"KIH-bee"; "mebi" would be "MEH-bee", and so forth.
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