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

Contributor(s): David Gabel

Also see Kibi, mebi, gibi, tebi, pebi, and all that, which are relatively new prefixes designed to express power-of-two multiples.

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 multipliers 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.

This was last updated in April 2008

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What's the largest amount of data we'll be able to store on personal devices in the next decade?
More than just PETABYTES, I think.
I believe PETA BYTE is the recommended Storage capacity for a personal devices in the coming Decade!
zetta-bytes, if we continue at the present rate, BUT if we find a need for storing more data it could accelerate or in the public finds that multi-tera-bytes are enough the pace will slow down. It is up to the "paying" public as to how fast the storage size will grow. (keep in mind that expansion is based on 2^ so each bit of address doubles the capacity of the storage)
It would probably not be more than a few terrabytes, everything else is store in the cloud space on some servers.
OK... there are couple of things to look at here. One is need and the other one is actual attainable capacity of a given technology. What is scientifically possible is different from what it can be mass produced and what will have a demand by either enterprise and residential users. For home users a few terabytes is more than enough compared to the need that folks like google or youtube will have.
1billion yottabytes evidently.

Seriously though perhaps a few Petabytes?
Are we talking theoretical or practical? Much of this depends on what we expect our devices to actually do. Theoretically, we could store petabytes of data on our devices, but I'd have to ask myself fundamentally why I would want to. It reminds me of the days when we had hundreds of gigabyte iPods, you know for those people that had to have every album they ever owned forever on one device, because they had a need to have months worth of continuous listening. Possible? Yes. Practical? Not really, especially with cloud storage and transfer capability. Could we be actively be storing terabytes of days in the next few years on our mobile devices? that seems a lot more likely, if for no other reason I'd not want that many eggs in just one basket.
100,1000 TB already exists so by 2020 peta byte 
what is the need for such huge storage in personal devices, while we will not be able to use 1 terabyte of data completely in one life time.
The future problems are not the Zettas or Exas. We don't have yet the OS's for that mass to crunch in "real time". We need multi-logistic, heuristic algorithmic processors. Like neurons, but with entanglement-controlled "fiering" of the units.


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