Byte

The byte (symbol: B or o, also known as the octet) is a unit of measurement of the size of information on a computer or other electronic device. The byte is eight bits. The bit is the smallest unit of storage on a computer, one on/off value.

One character in ASCII (for example, 'x' or '8') is stored in one byte. The character is held as a binary number which encodes a text character. To map each number to a character, an agreed code such as EBCDIC or ASCII is needed. EBCDIC is a character encoding used mainly on mainframe computers. It uses 8 bits per byte. ASCII is another encoding that only uses seven bits. Extended ASCII uses 8 bits to give more types of characters, mostly used on personal computers.

The byte is the smallest useful unit of measure to show how many characters a computer (or electronics device) can hold. This is useful for things like RAM, or storage devices like USB drives and other types of flash memory. Sending of data (for a modem or Wi-Fi) is usually measured in bits, not bytes.

On modern computers, one byte is equal to eight bits. Some early computers used fewer bits for each byte. To tell them apart, some computer scientists called the byte the octet. In modern usage, the octet and the byte are the same.

Symbol

The symbol for the byte is B. Sometimes a lowercase "b" is used, but this use is incorrect because "b" is actually the IEEE symbol for the bit. The IEC symbol for bit is bit. For example, "MB" means "megabyte" and "Mbit" means "megabit". The difference is important because the megabyte (MB) is 1 000 000 bytes, and 1 megabit (Mb or Mbit) is 1 000 000 bits or 125 000 bytes. It's easy to confuse the two, but the bit is much smaller than the byte, so the symbol b should be used when referring to the bit and an uppercase B when referring to the byte.

Byte Chart

According to the International Electrotechnical Commission (IEC), who sets many computer standards, these charts show how bytes should be referred to.

People who refer to 1 kilobyte as 1024 bytes, for example, are incorrect; 1024 bytes should be referred to as the kibibyte, according to the IEC. However, using 1024 for kilo and 1 048 576 for mega, etc. was widely practiced before the IEC standards were set in 1998. There is some confusion and mixing of terms in the marketplace. Computer memory is still commonly referred to in powers of 2, so people say the kilobyte of memory is 1024 bytes, whereas in computer data storage powers of 10 are used, so the kilobyte is 1000 bytes.

"kilo-" = 1000

When using standard metric names like "kilo-", "mega-" and "giga-", they should follow the same measure that other metric measurements use, like the kilometer (1 kilometer is 1000 meters), or the gigahertz (1 gigahertz is 1 000 000 000 hertz) for example.

Unit	Number	Short scale	Long scale	Scientific,E Notation/ Power of 10
Byte (B)	1	1 byte	1 byte	1*100,1E0 / 100
Kilobyte (KB)	1000	1 thousand bytes	1 thousand bytes	1*103,1E3 / 103
Megabyte (MB)	1 000 000	1 million bytes	1 million bytes	1*106,1E6 / 106
Gigabyte (GB)	1 000 000 000	1 billion bytes	1 billion bytes	1*109,1E9 / 109
Terabyte (TB)	1 000 000 000 000	1 trillion bytes	1 trillion bytes	1*1012,1E12 / 1012
Petabyte (PB)	1 000 000 000 000 000	1 quadrillion bytes	1 quadrillion bytes	1*1015,1E15 / 1015
Exabyte (EB)	1 000 000 000 000 000 000	1 quintillion bytes	1 quintillion bytes	1*1018,1E18 / 1018
Zettabyte (ZB)	1 000 000 000 000 000 000 000	1 sextillion bytes	1 sextillion bytes	1*1021,1E21 / 1021
Yottabyte (YB)	1 000 000 000 000 000 000 000 000	1 septillion bytes	1 septillion bytes	1*1024,1E24 / 1024
Ronnabyte (RB)	1 000 000 000 000 000 000 000 000 000	1 octillion bytes	1 octillion bytes	1*1027,1E27 / 1027
Quettabyte (QB)	1 000 000 000 000 000 000 000 000 000 000	1 nonillion bytes	1 nonillion bytes	1*1030,1E30 / 1030

"kibi-" = 1024

Since computers are very complex digital devices that are based on the binary numeral system rather than the commonly-used decimal numeral system or binary coded decimal system, there are many situations where the standard metric system does not work well, particularly with memory sizes for a computer or storage device. If a memory or storage device uses a binary number for addresses, the number of different positions to be accessed (the size of the memory) can be expressed as a power of 2, rather than a power of 10.

Unit	Number	Maths
Byte (B)	1	20 bytes
Kibibyte (KiB)	1024	210 bytes
Mebibyte (MiB)	1 048 576	220 bytes
Gibibyte (GiB)	1 073 741 824	230 bytes
Tebibyte (TiB)	1 099 511 627 776	240 bytes
Pebibyte (PiB)	1 125 899 906 842 624	250 bytes
Exbibyte (EiB)	1 152 921 504 606 846 976	260 bytes
Zebibyte (ZiB)	1 180 591 620 717 411 303 424	270 bytes
Yobibyte (YiB)	1 208 925 819 614 629 174 706 176	280 bytes
Robibyte (RiB)	1 237 940 039 285 380 274 899 124 224	290 bytes
Quebibyte (QiB)	1 267 650 600 228 229 401 496 703 205 376	2100 bytes