Byte, bit, nybble

excerpts from the Jargon File (VERSION 4.1.4, 17 JUN 1999):

byte /bi:t/ n.

[techspeak] A unit of memory or data equal to the amount used to represent one character; on modern architectures this is usually 8 bits, but may be 9 on 36-bit machines. Some older architectures used `byte' for quantities of 6 or 7 bits, and the PDP-10 supported `bytes' that were actually bitfields of 1 to 36 bits! These usages are now obsolete, and even 9-bit bytes have become rare in the general trend toward power-of-2 word sizes.

Historical note: The term was coined by Werner Buchholz in 1956 during the early design phase for the IBM Stretch computer; originally it was described as 1 to 6 bits (typical I/O equipment of the period used 6-bit chunks of information). The move to an 8-bit byte happened in late 1956, and this size was later adopted and promulgated as a standard by the System/360. The word was coined by mutating the word `bite' so it would not be accidentally misspelled as bit. See also nybble.

bit n.

[from the mainstream meaning and `Binary digIT'] 1. [techspeak] The unit of information; the amount of information obtained by asking a yes-or-no question for which the two outcomes are equally probable. 2. [techspeak] A computational quantity that can take on one of two values, such as true and false or 0 and 1. 3. A mental flag: a reminder that something should be done eventually. "I have a bit set for you." (I haven't seen you for a while, and I'm supposed to tell or ask you something.) 4. More generally, a (possibly incorrect) mental state of belief. "I have a bit set that says that you were the last guy to hack on EMACS." (Meaning "I think you were the last guy to hack on EMACS, and what I am about to say is predicated on this, so please stop me if this isn't true.")

"I just need one bit from you" is a polite way of indicating that you intend only a short interruption for a question that can presumably be answered yes or no.

A bit is said to be `set' if its value is true or 1, and `reset' or `clear' if its value is false or 0. One speaks of setting and clearing bits. To toggle or `invert' a bit is to change it, either from 0 to 1 or from 1 to 0. See also flag, trit, mode bit.

The term `bit' first appeared in print in the computer-science sense in 1949, and seems to have been coined by early statistician and computer scientist John Tukey. Tukey records that it evolved over a lunch table as a handier alternative to `bigit' or `binit'.

nybble /nib'l/ (alt. `nibble') n.

[from v. `nibble' by analogy with `bite' => `byte'] Four bits; one hex digit; a half-byte. Though `byte' is now techspeak, this useful relative is still jargon. Compare byte; see also bit. The more mundane spelling "nibble" is also commonly used. Apparently the `nybble' spelling is uncommon in Commonwealth Hackish, as British orthography would suggest the pronunciation /ni:'bl/.

Following `bit', `byte' and `nybble' there have been quite a few analogical attempts to construct unambiguous terms for bit blocks of other sizes. All of these are strictly jargon, not techspeak, and not very common jargon at that (most hackers would recognize them in context but not use them spontaneously). We collect them here for reference together with the ambiguous techspeak terms `word', `half-word' and `double word'; some (indicated) have substantial information separate entries.

2 bits:
crumb, quad, quarter, tayste
4 bits:
5 bits:
10 bits:
16 bits:
playte, chawmp (on a 32-bit machine), word (on a 16-bit machine), half-word (on a 32-bit machine).
18 bits:
chawmp (on a 36-bit machine), half-word (on a 36-bit machine)
32 bits:
dynner, gawble (on a 32-bit machine), word (on a 32-bit machine), longword (on a 16-bit machine).
word (on a 36-bit machine)
48 bits:
gawble (under circumstances that remain obscure)
64 bits
double word (on a 32-bit machine)

The fundamental motivation for most of these jargon terms (aside from the normal hackerly enjoyment of punning wordplay) is the extreme ambiguity of the term `word' and its derivatives.

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