Bit, Nibble, Byte

Where the three words came from

Bit is the oldest, and the only one of the three coined to shorten something people were already writing out. John Tukey contracted "binary digit" to "bit" in a Bell Labs memo on 9 January 1947. Claude Shannon put it into the literature the following year in A Mathematical Theory of Communication, and credited Tukey for it there.

Byte was coined by Werner Buchholz in 1956, during the design of the IBM 7030, the machine everyone called Stretch. He spelled it with a y deliberately, so that a typo could not turn it into "bit". On Stretch a byte was not eight bits: it was whatever you addressed, anywhere from one to eight.

Nibble is a pun. A byte sounds like a bite, so half of one is a nibble. It is credited to David Benson around 1958 and does not show up in print much before the mid-1970s. It survived because it turned out to name something real: four bits is exactly one hexadecimal digit.

Why this comes after Shannon on the timeline

The order looks wrong. Bitwise sits at 1937, ten years earlier, and it is about pushing bits around. How can the operations predate the word for the thing they operate on?

Because they did. Shannon showed in 1937 that a relay circuit is a piece of algebra, and engineers spent the next decade building machines that added, shifted and masked binary digits. They just wrote out binary digit every time, or said "pulse", or "position", or nothing at all.

Names arrive late, when someone gets tired of the long version or needs to draw a line that was not there before. Tukey was tired of writing binary digit. Buchholz needed a word for however many bits an instruction reached at once, and that only became a question when Stretch let each instruction pick a different number. Nobody wanted a word for four bits until hexadecimal made four bits worth exactly one character.

So the gap between 1937 and 1947 is not a gap in the engineering. It is the gap between doing something and finding it worth naming.

Why eight

Eight was an argument, not a discovery. IBM's SPREAD task force recommended the eight-bit byte in December 1961, and it was settled when System/360 was announced on 7 April 1964. Fred Brooks, its architect, pushed for eight against internal pressure to make it four or six, which would have been cheaper.

The case for eight was partly that ASCII had just landed on seven bits. Eight held a character with one bit left over, and it made a byte hold 256 distinct values, which is enough for a character set with room to grow. Six would not have. Every machine since has inherited that argument.

Why your machine picked a base

An octal digit is three bits. A hex digit is four. So a machine whose word size divides by three reads naturally in octal, and a machine built out of eight-bit bytes reads naturally in hex. That is the whole rule, and it explains a split that looks like tribal preference from the outside.

DEC's PDP-8 had a 12-bit word and its programmers wrote octal, because twelve is four octal digits exactly. The PDP-10's 36-bit word is twelve octal digits exactly. System/360 addressed eight-bit bytes, and two hex digits are exactly one byte, so its programmers wrote hex. Hex won in the end because the byte won.

The rule is only divisibility, and the switcher above is set up to prove it rather than to flatter it. Six bits and eighteen bits divide by three and not by four, so hex is the ragged one there. Twelve divides by both, so a PDP-8 word reads cleanly either way: four octal digits or three hex digits. Octal did not suit "old machines" and hex "new" ones; each suited the widths it divided.

The budget this page names is the one Morse, Baudot and the punch card had all been paying for a century without a word for it. Eight is where it settled.