Kilo Mega Giga Tera Peta Exa
Landers Hoang
Kilo, mega, giga, tera, peta, exa and zetta are among the binary prefixes used to denote the quantity of something, such as a byte or bit in computing and telecommunications. Sometimes called prefix multipliers, these prefixes are also used in electronics and physics.
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. For example, 1 kilobit per second (kbps) is equal to 103, or 1,000 bits per second (bps); 1 megabit per second (Mbps) 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.
The choice of power-of-10 versus power-of-two prefix multipliers can appear random. It helps to remember that multiples of bits are almost always expressed in powers of 10, while multiples of bytes are usually expressed in powers of two. Data speed is rarely expressed in bytes per second, and data storage or memory is seldom expressed in bits.
Giga comes from the Greek word for giant, and the first use of the term is believed to have taken place at the 1947 conference of the International Union of Pure and Applied Chemistry. Tera (1 trillion) comes from the Greek word teras or teratos, meaning "marvel, monster," and has been in use since approximately 1947.
The prefixes exa (1 quintillion) and peta (1 quadrillion) were added to the International System of Units (SI) in 1975. However, the origin and history of peta with data measurement terms is unclear. Zetta (1 sextillion) was added to the SI metric prefixes in 1991.
A gigabyte (GB) is equivalent to about 1 billion bytes. There are two standards for measuring the number of bytes in a gigabyte: base-10 and base-2. Base-10 uses the decimal system to show that 1 GB equals one to the 10th power of bytes, or 1 billion bytes. This is the standard most data storage manufacturers and consumers use today. Computers typically use the base-2, or binary, form of measurement. Base-2 has 1 GB as equal to 1,073,741,824 bytes. The discrepancy between base-10 and base-2 measurements became more distinct as vendors began to manufacture data storage media with more capacity.
In his book, The Singularity is Near, futurist Raymond Kurzweil estimated the capacity of a human being's functional memory to be 1.25 TB. This means that the memories of 800 human beings fit into 1 PB of storage.
If the average MP3 encoding is approximately 1 MB per second (MBps), and the average song lasts about four minutes, then a petabyte of songs could play continuously for more than 2,000 years. If the average smartphone camera photo is 3 MB, and the average printed photo is 8.5-inches wide, a petabyte of photos placed side by side would be more than 48,000 miles long. That is almost long enough to wrap around the equator twice.
To count all the bits in 1 PB of storage at a rate of 1 bps would take 285 million years, according to data analysts from Deloitte Analytics. A bit is a binary digit, either a 0 or 1; a byte is eight binary digits long.
A unit prefix is a specifier or mnemonic that is prepended to units of measurement to indicate multiples or fractions of the units. Units of various sizes are commonly formed by the use of such prefixes. The prefixes of the metric system, such as kilo and milli, represent multiplication by positive or negative powers of ten. In information technology it is common to use binary prefixes, which are based on powers of two. Historically, many prefixes have been used or proposed by various sources, but only a narrow set has been recognised by standards organisations.
Although formerly in use, the SI disallows combining prefixes; the *microkilogram or *centimillimetre, for example, are not permitted. Prefixes corresponding to powers of one thousand are usually preferred, however, units such as the hectopascal, hectare, decibel, centimetre, and centilitre, are commonly used. The unit prefixes are always considered to be part of the unit, so that, e.g., in exponentiation, 1 km2 means one square kilometre, not one thousand square metres, and 1 cm3 means one cubic centimetre, not one hundredth of a cubic metre.
In general, prefixes are used with any metric unit, but may also be used with non-metric units. Some combinations, however, are more common than others. The choice of prefixes for a given unit has often arisen by convenience of use and historical developments. Unit prefixes that are much larger or smaller than encountered in practice are seldom used, albeit valid combinations. In most contexts only a few, the most common, combinations are established. For example, prefixes for multiples greater than one thousand are rarely applied to the gram or metre.
In the specifications of hard disk drive capacities and network transmission bit rates, decimal prefixes are used. For example, a 500-gigabyte hard drive holds 500 billion bytes, and a 100-megabit-per-second Ethernet connection transfers data at 100 million bits per second. The ambiguity has led to some confusion and even lawsuits from purchasers who were expecting 220 or 230 and considered themselves shortchanged by the seller. (see Orin Safier v. Western Digital Corporation and Cho v. Seagate Technology (US) Holdings, Inc.).[8][9] To protect themselves, some sellers write out the full term as "1000000".
With the aim of avoiding ambiguity the International Electrotechnical Commission (IEC) adopted new binary prefixes in 1998 (IEC 80000-13:2008 formerly subclauses 3.8 and 3.9 of IEC 60027-2:2005). Each binary prefix is formed from the first syllable of the decimal prefix with the similar value, and the syllable "bi". The symbols are the decimal symbol, always capitalised, followed by the letter "i". According to these standards, kilo, mega, giga, et seq. should only be used in the decimal sense, even when referring to data storage capacities: kilobyte and megabyte denote one thousand and one million bytes respectively (consistent with the metric system), while terms such as kibibyte, mebibyte and gibibyte, with symbols KiB, MiB and GiB, denote 210, 220 and 230 bytes respectively.[10]
qemu-system-x86_64: -m 1.00000GiB: Parameter 'size' expects a non-negative number below 2^64
Optional suffix k, M, G, T, P or E means kilo-, mega-, giga-, tera-, peta-
and exabytes, respectively.
Can qemu behave more like virsh then? That would be ideal IMHO. I prefer to specify my RAM in powers of 2 and disk in powers of 10 so that when I test virtually using qemu I more closely match the exact constraints of real hardware. For the embedded work I do fitting in tight confines, it can make a significant difference.
(I actually to this with a wrapper I have around qemu, which is why you see a floating point value for GiB in my example above. My wrapper behaves like virsh and takes any *B, *iB format and regurgitates it into something qemu accepts.)
My Macbook has more than a 'Terabyte' of storage. What, I wondered, does 'Tera' mean, and what about all the other prefix words? Most of them come from Ancient Greek, but with some interesting twists. Here's a quick run through their history.
103 KILO - From chilioi meaning 'thousand'. It was introduced by the French in 1799, when the kilogram became the first official metric measure of mass (in some Victorian philosophy and science books it was referred to as the 'chiliogram'). A kilobyte is actually 1024 (or 210) bytes, but it's close enough to 1000 that the kilo prefix is still used.
106 MEGA - From megas meaning 'big' or 'tall', its first widespread use as a prefix may have been in 1821 to name the Megalosaurus, a giant lizard whose fossilised bones had been found near Oxford. Mega was introduced as a scientific prefix in 1868 (there are mentions of MegaOhms of resistance) , though it didn't become an official SI Prefix until 1960. These days it is most frequently encountered in Megabytes (big computer images) and MegaHertz (on FM radio).
109 GIGA - From gigas meaning 'giant', it is said that giga was first proposed as a prefix in Germany in the 1920s. It became an official SI prefix in 1960, but there were different opinions on how to pronounce it. In the 1985 film Back To The Future, Marty asks the eccentric scientist Doc Brown: 'What the hell is a jigga-watt?'. The pronunciation became Giga with a hard G in the 1990s (though the French still pronounce it 'zhiga', as in Dr Zhivago).
1012 TERA - From tera meaning 'monster'. No, there is no connection to ptero (like pterodactyl) which means 'winged'. Tera was introduced as a prefix in 1960, along with Mega and Giga. Coincidentally, this is the fourth prefix (it is 10004) and tera is very similar to tetra, the Greek word for four. This coincidence led to...
1015 PETA - In the 1970s, as scientists and computer technologists started dealing with measurements at a higher order of magnitude the International Bureau needed prefixes that would cope with the bigger numbers. They opted for Peta because it is like penta, but with a dropped letter (in the spirit of tera and tetra). There are allegedly two Petabytes of data stored in all the US research libraries combined.
1021 ZETTA - in 1982, New Scientist published an article about the likely need for a higher, seventh prefix. I now make a fleeting appearance in the story. I submitted a letter (see here) suggesting they continue the pattern of dropping a consonant, making Hepta into Hepa, pronounced Heepa, as in 'That's a Hepajoules!' (geddit?). Not surprisingly they ignored my suggestion, and in 1991 they decided to make the prefix for 10007 Zetta, derived from the letter Zeta, which the Greeks used for the number seven. (Confusingly, zeta is the sixth letter in the Greek alphabet). By the way, Zeta led to the Roman's word 'Septa', or seven. September used to be the seventh month, before the two Caesars, Julius and Augustus, decided to insert their own months in front of it.
d3342ee215