Where Did Kilo, Mega, Giga and All Those Other Prefixes Come From?

They have entered our language. Everyone uses them. The terms, particularly with "byte", are almost commonplace. Kilobyte, Megabyte and Gigabyte are part of our lexicon.

But do you know where they came from?

First, let's show the terms:

Kilo	10001	103	1,000
Mega	10002	106	1,000,000
Giga	10003	109	1,000,000,000
Tera	10004	1012	1,000,000,000,000
Peta	10005	1015	1,000,000,000,000,000
Exa	10006	1018	1,000,000,000,000,000,000
Zetta	10007	1021	1,000,000,000,000,000,000,000
Yotta	10008	1024	1,000,000,000,000,000,000,000,000

 

Ok. So where did they come from?

Kilo comes from the Greek khiloi and means, curiously enough, 1000. It is interesting enough, the only prefix with a direct numerical meaning.

The next three come from Greek and Latin and are either descriptive or mythological.

Mega comes from the Greek mega meaning "great", as in "Alexandros O Megas" or "Megas Alexandros" (Alexander the Great).

Giga comes from Latin gigas meaning "giant".

Tera comes from Greek teras meaning "monster".

Now we return to numbers. Though not direct numerical references, the next two are indirect references.

Peta comes from the Greek pente meaning five. This is the fifth prefix (for 1000⁵). This term, and the next one, were both added in 1975 by the General Conference of Weights and Measures (abbreviated CGMP because it is in France)

Exa comes from Greek hex meaning six. This is the sixth prefix (for 1000⁶). Taking "Hexa" and making the "H" silent (as it is in France, home of  the CGMP) gives "Exa".

Here we leave the numerical references again. Unable to return to the mythological (after great, giants and monsters what else is there), we move to the Latin alphabet. For reasons I don't know, we start with the last letter (Zetta), working backwards to the beginning.

Zetta, often mistaken for the Greek Zeta, is the last letter of the Latin alphabet. This prefix and the next one were added in 1990 by CGMP.

Yotta is the penultimate (next to last) letter of the Latin alphabet.

Kilo, mega, giga, tera, peta, and all that

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 in increments of three orders of magnitude (10³ or 1,000). In IT and data storage, multipliers are defined in powers of 2 from 2¹⁰ to 2⁸⁰, 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 *	--
micro-	m	10-6 *	--
milli-	m	10-3 *	--
centi-	c	10-2 *	--
deci-	d	10-1 *	--
(none)	--	100	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
* Not generally used to express data speed
** k = 103 and K = 210

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 to 10³, or 1,000, bps (bits per second); 1 Mbps (one megabit per second) is equal to 10⁶, or 1,000,000, bps. (The 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, power-of-2 multipliers are used. Technically, the uppercase K should be used for kilo- when it represents 2¹⁰. Therefore 1 KB (one kilobyte) is 2¹⁰, or 1,024, bytes; 1 MB (one megabyte) is 2²⁰, 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.