Glossary: BIT and BYTE
In binary code there are two digits 0 and 1. A bit is either the 'off' digit 0 or the 'on' digit 1.
- A bit (symbol: bit or b) is a Binary digIT
- A byte (symbol: B) is coding unit made up of eight bits - e.g. 00101011. It can be expressed more compactly in hexadecimal as two digits - e.g. 2B
Multiple bits and bytes
SI prefixes are a shorthand way in which multiples of terms are expressed in science. In computing there is a similar system from the IEC
|
Binary
value |
IEC binary prefixes |
Name
(Symbol) |
Value |
Name
(Symbol) |
Value |
kilobit (kbit) |
103 |
210 |
kibibit (Kibit) |
210 |
megabit (Mbit) |
106 |
220 |
mebibit (Mibit) |
220 |
gigabit (Gbit) |
109 |
230 |
gibibit (Gibit) |
230 |
terabit (Tbit) |
1012 |
240 |
tebibit (Tibit) |
240 |
petabit (Pbit) |
1015 |
250 |
pebibit (Pibit) |
250 |
exabit (Ebit) |
1018 |
260 |
exbibit (Eibit) |
260 |
zettabit (Zbit) |
1021 |
270 |
zebibit (Zibit) |
270 |
yottabit (Ybit) |
1024 |
280 |
yobibit (Yibit) |
280 |
There can never be a smaller unit of data than a 'bit' - you will therefore never get centibits or millibits!
There are several commonly used multiples of bit expressions that are used as units of information:
- byte (8 bits),
- kilobit (either 1000 or 210 = 1024 bits)
- megabyte (either 8 000 000 or 8×220 =8 388 608 bits), etc.
Computers usually manipulate bits in groups of a fixed size, conventionally named "words". The number of bits in a word varies with the hardware design of the computer model - see register.
Approved abbreviations
The International Electrotechnical Commission's standard IEC 60027 specifies that the symbol for binary digit should be "bit", and this should be used in all multiples, such as "kbit" (for kilobit). However, the letter "b" (in lower case) is widely used too.
The letter "B" (upper case) is both the standard and customary symbol for byte.
Therefore - just as in science - the case of the letter you use matter!
Derived units: data transfer rate
In telecommunications (including computer networks), data transfer rates are usually measured in bits per second (bit/s) or its multiples, such as kbit/s. (This unit is not to be confused with baud.) As this is a compound unit - that of information units divided by time - you can get millibits per second - very slow rate!
