Computer Numbers
Mega-which? Giga-what? Common Computer
Measurements
I commonly receive questions from people shopping for computers about what
words like Megabytes (MB) and GigaHertz (GHz) mean.
Here are some of the most common terms you may see or hear when shopping for a
computer.
- CPU stands for Central Processing Unit, another name for the
computer's processor or "brain". Some people use CPU in a
generic way to mean the box (desktop or tower) that houses the computer's
brain. This box is more accurately described as the "system
unit" because it contains a lot more than just the CPU, but many people
don't use the term "system unit". An ad for a computer that
says 2.4 GHz CPU means the computer has a 2.4 GHz processor. (See
GigaHertz below.)
- Gigabytes (GB) is a measure of computer storage. This
usually tells you how large a hard drive is. An ad for a computer with
a 30 GB hard drive (sometimes listed as 30 GB HD) means the computer's hard
drive can store about 30 billion bytes of information. If you are
planning to use lots of pictures, buy a larger hard drive instead of a
smaller one. If you are planning to do video editing, buy as large of
a hard drive as you can.
- GigaHertz (GHz) is a measure of processor speed equal to
1,000,000,000 cycles per second. An ad for a computer that says 2.4
GHz processor means that computer's processor (computer "brain")
operates at 2,400,000,000 cycles per second.
- Megabytes (MB) is a measure of computer storage. This
usually tells you how large the computer's memory (RAM or temporary storage)
is for running programs or processing images or video. An ad for a
computer that says 256 MB RAM means the computer's temporary memory is about
256 million bytes. More memory is better, especially if you are
processing images. Get as much memory as you can for processing video.
- ISP stands for Internet Service Provider. This may be
a larger service like AOL, MSN, or Earthlink, or a smaller local company
that provides access to the Internet.
- Kilobit (Kb) is the transmission speed of a dial-up (phone
line) modem equal to 1024 bits per second.
- Megabit (Mb) is the transmission speed of a broadband (DSL
or Cable) modem equal to about 1,000,000 bits per second.
(Technically, it's 1,048,576.)
- Gigabit (Gb) is the transmission speed of a broadband (DSL
or Cable) modem equal to about 1,000,000,000 bits per second.
(Technically, it's 1,073,741,824.)
For further information about how
things in computers are counted and measured, see below.
Part of the confusion between humans and computers comes from
having multiple number systems.
- Binary is the typical number system used by computers. The binary number system consists of
just two digits: zero and one. This two-digit numbering system is also
known as "Base 2". This system can seem foreign to
people who typically use the decimal or Base 10 numbering system.
- Decimal is the typical number system used by humans. The
decimal number system consists of ten digits: zero through nine. This
ten-digit numbering system is also known as "Base
10".
- Hexadecimal is a numbering system that translates more easily to
binary (Base 2) than decimal (Base 10) does. The hexadecimal numbering
system consists of sixteen digits: 0-9 and A-F. This
sixteen-digit numbering system is also known as "Base 16". typically used to represent
larger computer numbers, or the contents of computer storage.
- For further information on Number Systems, see below.
- Bit (b, lower case b) is short for a single binary digit.
A bit is a single number, 0 or 1, in binary. In the computer world,
bits are often used to denote data transmission speeds over a modem
or a digital connection.
- Byte (B, upper case B) is a measure of computer storage meaning 8 bits. Since a byte has 8 binary digits, it can have 2 to the eighth
power (28) values, or 256 values. Since the computer starts
counting at zero, the value of a single byte of information can range from 0
to 255. This is typically enough to hold a single character in a word
processing document, such as the letter "A" that has an ASCII
decimal value of 65 (which converted to hexadecimal is 41, or is 01000001 in
binary). Word processing
documents are typically much larger, though, because they can also hold
formatting, layout, and font information, as well as graphics or clip art in
addition to simple text. In the computer world, bytes are often used
to denote data storage capacity.
- Kilobyte (KB) means 2 to the 10th power (210)
bytes, or 1024 bytes. Notice that when byte is abbreviated it becomes
a capital "B" for "bytes". A lower case
"b" denotes "bits", which is one-eighth of a byte, hence
the smaller lower-case letter.
- Megabyte (MB) means 2 to the 10th power (220)
bytes, or 1,048,576 bytes. This is NOT exactly and simply a million
(106 or 1,000,000) bytes, as some people suppose it to be.
Do not confuse the term megabyte with megabit. Since a byte is 8 bits,
a megabyte (MB) is 8 times larger than a megabit (Mb).
The memory storage (RAM) on most home computers is measured in megabytes
(MB). Transmission of data on high-speed connections, such as a DSL or
a cable modem, is measured in megabits per second (Mbps).
- Gigabyte (GB) means 2 to the 30th power (230)
bytes, or 1,073,741,824 bytes. Again, this is NOT simply a billion (109
or 1,000,000,000) bytes. The disk storage (hard drive or HD) on most
home computers is measured in gigabytes (GB).
- Terabyte (TB) means 2 to the 40th power (240) bytes, or
1,099,511,627,776. This is not to be confused with the human term
trillion (1012 or 1,000,000,000,000).
- Hertz (Hz) means a unit of frequency of one cycle per
second. This is typically used as a measurement of the speed of the
processor, usually reported in MegaHertz or GigaHertz.
- MegaHertz (Hz) means one million cycles per second.
- GigaHertz (Hz) means one billion (American) cycles per
second, or one thousand million (British) cycles per second.
- Common Computer Number Prefixes: Below is a chart with
English equivalents for various computer number prefixes.
| Prefix |
Symbol |
Origin |
American
English |
British
English |
| kilo- |
K |
Greek khilioi
'thousand' |
thousand |
thousand |
| mega- |
M |
Greek megas
'great' |
million |
million |
| giga- |
G |
Greek gigas
'giant' |
billion |
thousand million
(or
"milliard") |
| tera- |
T |
Greek teras
'monster' |
trillion |
billion |
| peta- |
P |
Greek pente
'five' |
quadrillion |
thousand billion |
| exa- |
E |
Greek hex 'six' |
quintillion |
trillion |
| zetta- |
Z |
Italian sette
'seven' |
sextillion |
thousand trillion |
| yotta- |
Y |
Italian otto
'eight' |
septillion |
quadrillion |
- International Number Prefixes (SI): The magnifying prefixes for various measurements in
human and computer number systems today are derived from the Système
Internationale (SI) or International System of mathematical and
scientific numbers as maintained by the Bureau
International des Poids et Mesures (BIPM). Magnitudes in most
areas of human endeavor are based on powers of 1000, which comes from Base
10. Magnitudes in the computer worlds come from 1024, which comes from
Base 2, since 210=1024. Below is a table of common
magnitudes with their corresponding binary interpretations in common use.
| SI
Prefix |
Symbol |
Power
of 1000 |
Power
of 1024 |
Power
of 2 |
Decimal
Equivalent |
| kilo- |
k / K * |
k=10001 |
K=10241 |
210 |
1,024 |
| mega- |
M |
10002 |
10242 |
220 |
1,048,576 |
| giga- |
G |
10003 |
10243 |
230 |
1,073,741,824 |
| tera- |
T |
10004 |
10244 |
240 |
1,099,511,627,776 |
| peta- |
P |
10005 |
10245 |
250 |
1,125,899,906,842,624 |
| exa- |
E |
10006 |
10246 |
260 |
1,152,921,504,606,846,976 |
| zetta- |
Z |
10007 |
10247 |
270 |
1,180,591,620,717,411,303,424 |
| yotta- |
Y |
10008 |
10248 |
280 |
1,208,925,819,614,629,174,706,176 |
* The symbol of a lower case "k" is used by BIPM
to denote 1000, not 1024. In the computer world, a capital "K"
is used to denote 1024. The BIPM deprecates the use of the SI prefixes
for powers of two. Also, in data transfer rates the prefixes stand for
powers of ten so, for example, 28.8 kb/s means 28,800 bits per second.
In another example, 3.5" floppy disks are often described as storing
"1.44 MB". In fact, the correct size is 1440 KB = 1440 * 1024 =
1,474,560 bytes.
- AskOxford:
How many is a billion? - Study the different uses of the word
"billion" between American and British people.
- Base
Valued Numbers - A discussion of number bases (including 2, 5, 8,
10, 12, 16, 20, and 60) and their various uses.
- Billion,
A U.K. View - Find out the differences in usage between an American
Billion and a traditional British Billion.
- Bureau International des Poids et
Mesures (BIPM)
- "International Bureau of Weights and Measures" - Read more about the the Système
Internationale (SI) or International System of mathematical and
scientific numbers.
- Latin
Numbers: About.com - Words for Latin numbers from 1-10, then
100-1000 by 100's, and 2000
- Latin
Numbers: Guide - A guide to Latin numerals, including cardinal,
ordinal, distributive, and adverb forms
- Latin
Numbers: Reference Table - Includes 1-10, then 100-1000 by 100's,
2000, ten thousand, one hundred thousand, and one million
- Merriam-Webster:
Metric System Table
- Merriam-Webster:
Number Table - A table of cardinal and ordinal numbers, as well as
American and British number systems for numbers over a million.
- Merriam-Webster:
Weights and Measures Table
- NIST Guide
to SI Units - National Institute of Standards and Technology guide
and tables on International System units or the MKS (meter-kilogram-second)
system.
- TechEncyclopedia:
Space/Time
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