Bit-paired Keyboard N.,obs. (alt. `bit-shift Keyboard') A Non-standard Keyboard Layout That Seems To Have Originated With The Teletype ASR-33 And Remained Common For Several Years On Early Computer Equipment.

Home › Fortune Cookies › Jargon File

bit-paired keyboard n.,obs.

(alt. `bit-shift
keyboard') A non-standard keyboard layout that seems to have
originated with the Teletype ASR-33 and remained common for several
years on early computer equipment. The ASR-33 was a mechanical
device (see EOU), so the only way to generate the character
codes from keystrokes was by some physical linkage. The design of
the ASR-33 assigned each character key a basic pattern that could
be modified by flipping bits if the SHIFT or the CTRL key was
pressed. In order to avoid making the thing even more of a kluge
than it already was, the design had to group characters that shared
the same basic bit pattern on one key.

Looking at the ASCII chart, we find:

high low bits
bits 0000 0001 0010 0011 0100 0101 0110 0111 1000 1001
010 ! " # $ % & ' ( )
011 0 1 2 3 4 5 6 7 8 9


This is why the characters !"#$%&'() appear where they do on a
Teletype (thankfully, they didn't use shift-0 for space). The
Teletype Model 33 was actually designed before ASCII existed, and
was originally intended to use a code that contained these two
rows:

low bits
high 0000 0010 0100 0110 1000 1010 1100 1110
bits 0001 0011 0101 0111 1001 1011 1101 1111
10 ) ! bel # $ % wru & * ( " : ? _ , .
11 0 1 2 3 4 5 6 7 8 9 ' ; / - esc del


The result would have been something closer to a normal keyboard. But
as it happened, Teletype had to use a lot of persuasion just to keep
ASCII, and the Model 33 keyboard, from looking like this instead:

! " ? $ ' & - ( ) ; : * / , .
0 1 2 3 4 5 6 7 8 9 + ~ < > × |


Teletype's was not the weirdest variant of the QWERTY layout
widely seen, by the way; that prize should probably go to one of
several (differing) arrangements on IBM's even clunkier 026 and 029
card punches.

When electronic terminals became popular, in the early 1970s, there
was no agreement in the industry over how the keyboards should be
laid out. Some vendors opted to emulate the Teletype keyboard,
while others used the flexibility of electronic circuitry to make
their product look like an office typewriter. Either choice was
supported by the ANSI computer keyboard standard, X4.14-1971, which
referred to the alternatives as `logical bit pairing' and
`typewriter pairing'. These alternatives became known as
`bit-paired' and `typewriter-paired' keyboards. To a hacker,
the bit-paired keyboard seemed far more logical -- and because
most hackers in those days had never learned to touch-type, there
was little pressure from the pioneering users to adapt keyboards to
the typewriter standard.

The doom of the bit-paired keyboard was the large-scale
introduction of the computer terminal into the normal office
environment, where out-and-out technophobes were expected to use
the equipment. The `typewriter-paired' standard became
universal, X4.14 was superseded by X4.23-1982, `bit-paired'
hardware was quickly junked or relegated to dusty corners, and both
terms passed into disuse.

However, in countries without a long history of touch typing, the
argument against the bit-paired keyboard layout was weak or
nonexistent. As a result, the standard Japanese keyboard, used on
PCs, Unix boxen etc. still has all of the !"#$%&'() characters
above the numbers in the ASR-33 layout.

Related: