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byte

A unit of information in a binary digital computer, = 8 bits. Abbreviation, B (lowercase b is the abbreviation for bit). See Byte magazine, Sept. 1995, page 20.

An example of a byte, written as a binary number, would be “10101011”. It can have one of 2⁸, or 256, possible values, which is enough to store, for example, any whole number from 0 to 255, or a single character of the alphabet in the ASCII code. Although the term was first used to refer to units of 6 bits, 7 bits and other values, depending on the machine, it was inexorably drawn to a value that was a power of 2. According to Eric Raymond (in his wonderful New Hacker's Dictionary), the byte began to become standardized at 8 bits around 1956, and was fixed at 8 bits by the introduction of the IBM/360 computer. A few authorities, however, continue to regard the size of the byte as machine-dependent. See also nibble.

It has become usual to use “byte” with the metric prefixes “kilo-”, “mega-”, “tera-”, and “peta-”, but sometimes not with their usual meanings as decimal multipliers. For a recent official attempt to dispel this confusion, see prefixes for binary multiples.

Kilobyte

The kilobyte (symbol, K, KB, or, incorrectly, Kb) is not equal to 1,000 bytes, but rather to 1,024 (i.e., 2¹⁰) bytes, the power of 2 which is closest to 1,000. Present-day electronic computers represent information in binary notation; the signals can have only one of two values. The decimal number 1024 is a round number in binary notation: 10000000000. The decimal number 1000 (111110100 in binary) is not.

Megabyte

The term megabyte (symbol, MB or M) is used with three different meanings:

a) Computer designers and programmers working with bytes generally consider 1 megabyte = 1,024 kilobytes, or 1,048,576 bytes (= 2²⁰).

b) Vendors of hard disc drives and flash memory cards generally consider one megabyte = 1,000,000 bytes, a definition which is easier to understand and incidentally makes their drives look bigger. This megabyte is sometimes (but rarely) called a millionbyte or a decimal megabyte.

The use of the above two senses of “megabyte” in the same commercial activity continues to lead to confusion and hard feelings.

c) Finally, in giving the capacity of floppy disks, the megabyte was taken to be 1,000 kilobytes.

sources

Page 16: “Note: Western Digital and CHKDSK [a Microsoft utility--ed.] define a megabyte (MB) as 1,000,000 bytes. CMOS setup and some utility software define a megabyte as 1,048,576 bytes.”
Page 29: “Hard drive suppliers define a decimal megabyte as 1,000,000 bytes (10⁶). Alternatively, a binary megabyte is defined as 1,048,576 (2²⁰).”

Western Digital Caviar Series AC2540, AC2700, AC2850, AC31000 and AC31200 Quick Installation Guide (no date, but 1994 copyright).

Page 19: “With regard to your CMOS automatically calculating your drive capacity, keep in mind that most hard drives are technically rated in Millionbytes, whereas most CMOS setups display drive capacity in Megabytes. The formatted capacity of your new drive is the same regardless of what unit is used for measurement due to the fact that megabytes are simply a larger unit of measurement (1 Megabyte = 1.04858 Millionbytes).”

*GB = 1,000,000,000 bytes when referring to storage capacity; accessible capacity is less.

Advertisement by IBM for a personal computer. New Architect, volume 7, issue 03, footnote page 17. (March 2002)

Please remember that DVD media refers to a gigabyte of data as a pure 1 billion bytes, not the actual value which is 1,073,741,824 bytes. Therefore, the maximum amount of data that will fit on most current DVD media is about 4.4Gb.

Readme.html, installation file for PC Backup software from StompSoft, Inc, dated November 14, 2005.

gibibyte...GiB...GiB :=2³⁰ B = 1 073 741 824 B
...
gigabyte...GB...GB := 10⁹B

IEEE Std 260.1™-1004.
IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units).
Approved 22 July 2004, American National Standard Institute; approved 25 March 2004, IEEE-SA Standards Board.
New York: IEEE, 24 September 2004.

MB means one million bytes. GB means one billion bytes.

Footnote 8, describing the capacity of the hard drive in a video camera, in an advertising flier by the Sony Corporation delivered with the Los Angeles Times, 10 December 2007.

Disk Drive Companies such as SanDisk define 1 MEGABYTE as 1,000,000 BYTES.

SanDisk is a vendor of flash memory cards. From www.sandisk.com/Assets/Categories/Products/card_capacitydisclaimer.pdf, retrieved 10 December 2007.

Please note: For flash media devices, 1 megabyte = 1 million bytes; 1 gigabyte = 1 billion bytes.

From an advertisement by the flash memory manufacturer PNY in Digital Photo, vol. 13, no. 6 (Nov. 2009), page 7. The same wording appeared on PNY's packaging in 2011.