In computer terms a bit refers to a single 1 or 0 in a binary number. 8 bits taken as a single unit form a byte. 4 bits as a single unit form a nibble. Generally 16 bits (2 bytes) is referred to as a WORD, 32 bits (4 bytes) a DWORD (for double word), 64 bits 8 bytes a QWORD (for quad word).

More generally than a binary digit, a bit is a general unit for entropy or information. Given a random source with 2 possible equally-probable states (a fair coin), the best possible compression of the source's current state will be 1 bit (here "best" refers to the best average rate you can achieve even for long runs of the source; clearly if your source is A 99% of the time and B 1% of the time, you can compress a run of 1000 A's and B's to a lot less than 1000 bits; for instance, 10 bits suffice to give the location of each B or to say there are no more B's, which gives an average of 110 bits). So a fair coin toss gives 1 bit of information; its entropy is 1 bit.

More generally still, it is customary to measure any log odds ratio (any logarithm of the ratio of 2 probabilities) in bits! See the Naiman-Pearson lemma for an example of the use of such an odds ratio; since odds ratios have a huge dynamic range, taking a logarithm is a very "natural" thing to do. And the logarithm of a ratio is just the difference between the logarithms, so any log of the inverse of a probability is also measured in bits. What the Naiman-Pearson lemma says, when phrased this way, is that when trying to decide which of two probability distributions a sample came from, you should pick the distribution for which the sample gives less information. That explains the ratio appearing there. Of course, one of the distributions may be a lot more likely than the other, so choosing it requires a lot less information; taking into account the added information you get for choosing one distribution over the other gives the constant which appears in the lemma.

When natural logarithms are used, the result is in nats.

A 6502 instruction that performs a bitwise AND between A and a number but discards the result except to set the Z flag. It also sets S and V to bits 7 and 6 of the number.
  • Function: !(A & N) => Z; N >> 7 => S; N >> 6 => V
  • Updates flags: S V . . . . Z .
  • Opcode numbers:
    dp    $24
    abs   $2C

Super Mario Brothers's code often uses BIT to skip an instruction by fooling the processor into treating an instruction as an address, using code similar to this:

  ldx #$10
  .dcb $2c    ;skip next two-byte instruction
  ldx #$20
  lda #12
  sta iccom,x

See also: 6502 instructions | 6502 addressing modes

binary four = B = bit bang

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 a 1948 paper by information theorist Claude Shannon, and was there credited to the early computer scientist John Tukey (who also seems to have coined the term `software'). Tukey records that `bit' evolved over a lunch table as a handier alternative to `bigit' or `binit', at a conference in the winter of 1943-44.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

There just aren't enough writeups here...

A bit is also a piece of equipment used with horses. It is basically a what you stick in their mouths and the reins attatch. Horses have a spot in the back of their mouths which, for some strange reason, there are no teeth, although there are teeth in front of and behind this spot. The bit fits right into this spot. The most common material used today is stainless steel. You might also find bits made of copper or rubber. Typically copper is seldom used as it causes excessive salivation, and rubber is used on horses with more sensitive mouths.

The basic purpose of the bit is to serve as a means of communication between horse and rider, although in reality your legs are really the prime means of control in a properly trained horse. The horse is trained to respond to the various forces on the bit, if both sides are pulled back it means halt or slow down. If one side is pulled, it means to turn in that direction. Simple really.

Well, maybe not that simple... There are a lot of types of bits which offer various amounts of control, depending on the horse. The most common type is a snaffle, which is basically two pieces of steel jointed together in the middle so that it is flexible. When the reins are pulled back, the joint flexes and causes pressure to be placed on the roof of the mouth as an extra means of control. The middle piece may also be a straight bar or a straight bar with a raised area in the middle.

Now you've also got to consider the part of the bit that is outside the horses mouth. The most common type used in english riding is an egg butt, which features an egg shaped circle which the reins attatch to. In western bits, as well as some english bits such as a french snaffle, the outside part may have a shank which extends downward that the reins attatch to. This gives leverage which causes the bit to rotate in the horses mouth, brining the middle part up against the roof of the mouth.

On a final note, should you ever find yourself in control of a horse, keep in mind that this is a metal thing in it's mouth. Think how that would make you feel. It should be used as a way of indicating what you want, much like nudging someone to get them to move. You should NEVER jerk on the reins, when I see people do this I want to stick a bit in their mouth and yank it around to show them what it feels like...

Bit (&?;), n. [OE. bitt, bite, AS. bite, bite, fr. bItan to bite. See Bite, n. & v., and cf. Bit a morsel.]


The part of a bridle, usually of iron, which is inserted in the mouth of a horse, and having appendages to which the reins are fastened. Shak.

The foamy bridle with the bit of gold.


Fig.: Anything which curbs or restrains.


© Webster 1913

Bit, v. t. [imp. & p. p. Bitted (&?;); p. pr. & vb. n. Bitting.]

To put a bridle upon; to put the bit in the mouth of.


© Webster 1913


imp. & p. p. of Bite.


© Webster 1913

Bit, n. [OE. bite, AS. bita, fr. bItan to bite; akin to D. beet, G. bissen bit, morsel, Icel. biti. See Bite, v., and cf. Bit part of a bridle.]


A part of anything, such as may be bitten off or taken into the mouth; a morsel; a bite. Hence: A small piece of anything; a little; a mite.


Somewhat; something, but not very great.

My young companion was a bit of a poet.
T. Hook.

⇒ This word is used, also, like jot and whit, to express the smallest degree; as, he is not a bit wiser.


A tool for boring, of various forms and sizes, usually turned by means of a brace or bitstock. See Bitstock.


The part of a key which enters the lock and acts upon the bolt and tumblers. Knight.


The cutting iron of a plane. Knight.


In the Southern and Southwestern States, a small silver coin (as the real) formerly current; commonly, one worth about 12 1/2 cents; also, the sum of 12 1/2 cents.

Bit my bit, piecemeal. Pope.


© Webster 1913


3d sing. pr. of Bid, for biddeth. [Obs.] Chaucer.


© Webster 1913

Bit, n.

In the British West Indies, a fourpenny piece, or groat.


© Webster 1913

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