Eight bits is a byte
In most computer systems, a byte is a unit of information that is eight long. A byte is the unit most computers use to represent a character such as a letter, number, or typographic symbol (for example, "g", "5", or "?"). A byte can also hold a string of bits that need to be used in some larger unit for application purposes (for example, the stream of bits that constitute a visual image for a program that displays images).
In some computer systems, four bytes constitute a word, a unit that a computer processor can be designed to handle efficiently as it reads and processes each instruction. Some computer processors can handle two-byte or single-byte instructions.
A byte is abbreviated with a "B". (A bit is abbreviated with a small "b".) Computer storage is usually measured in byte multiples. For example, an 820 MB hard drive holds a nominal 820 million bytes of information. Byte multiples are based on powers of 2 and commonly expressed as a "rounded off" decimal number. For example, one megabyte ("one million bytes") is actually 1,048,576 (decimal) bytes. (Confusingly, however, some hard disk manufacturers and dictionary sources state that bytes for computer storage should be calculated as powers of 10 so that a megabyte really would be one million decimal bytes.)
Some language scripts require two bytes to represent a character. These are called double-byte character sets (DBCS).
1) As a measure of computer processor storage and real and virtual memory, a megabyte (abbreviated MB) is 2 to the 20th power or 1,048,576 bytes in decimal notation.
2) According to the IBM Dictionary of Computing, when used to describe disk storage capacity and transmission rates, a megabyte is 1,000,000 bytes in decimal notation.
According to the Microsoft Press Computer Dictionary, a megabyte means either 1,000,000 bytes or 1,048,576 bytes.
According to Eric S. Raymond in The New Hacker's Dictionary, a megabyte is always 1,048,576 bytes on the argument that bytes should naturally be computed in powers of two.
Iomega Corporation uses the decimal megabyte in calling the disk a "100MB disk" when it actually holds 100,431,872 bytes. If Iomega used the powers-of-two megabyte, the disk could be said to hold only 95.8 megabytes (if you divide 100,431,872 by 1,048,576).
A gigabyte (pronounced GIG-a-bite with hard G's) is a measure of computer data storage capacity and is "roughly" a billion bytes. A gigabyte is two to the 30th power, or 1,073,741,824 in decimal notation.
A terabyte is a measure of computer storage capacity and is 2 to the 40th power or, in decimal, approximately a thousand billion (that is, a thousand gigabytes).
A petabyte is a measure of memory or storage capacity and is 2 to the 50th power bytes or, in decimal, approximately a thousand .In recently announcing how many Fibre Channel storage arrays they had sold, Sun Microsystems stated that it had shipped an aggregate of two petabytes of storage or the equivalent of 40 million four-drawer filing cabinets full of text. IBM says that it has shipped four petabytes of SSA Storage.
An exabyte (EB) is a large unit of computer data storage, two to the sixtieth power. The prefix exa means one billion billion, or one quintillion, which is a decimal term. Two to the sixtieth power is actually 1,152,921,504,606,846,976 bytes in decimal, or somewhat over a quintillion (or ten to the eighteenth power) bytes. It is common to say that an exabyte is approximately one quintillion bytes. In decimal terms, an exabyte is a billion.