bit rot n.
[common] Also bit decay.
Hypothetical disease the existence of which has been deduced from
the observation that unused programs or features will often stop
working after sufficient time has passed, even if `nothing has
changed'. The theory explains that bits decay as if they were
radioactive. As time passes, the contents of a file or the code
in a program will become increasingly garbled.
There actually are physical processes that produce such
effects (alpha particles generated by trace radionuclides in
ceramic chip packages, for example, can change the contents of a
computer memory unpredictably, and various kinds of subtle media
failures can corrupt files in mass storage), but they are quite
rare (and computers are built with error-detecting circuitry to
compensate for them). The notion long favored among hackers that
cosmic rays are among the causes of such events turns out to be a
myth; see the cosmic rays
entry for details.
The term software rot is
almost synonymous. Software rot is the effect, bit rot the
notional cause.
Node:bit twiddling, Next:bit-paired keyboard,
Previous:bit rot, Up:= B =
bit twiddling n.
[very common] 1. (pejorative) An exercise in tuning (see tune) in which incredible amounts of time
and effort go to produce little noticeable improvement, often
with the result that the code becomes incomprehensible. 2.
Aimless small modification to a program, esp. for some pointless
goal. 3. Approx. syn. for bit
bashing; esp. used for the act of frobbing the device
control register of a peripheral in an attempt to get it back to
a known state.
Node:bit-paired keyboard,
Next:bitblt, Previous:bit twiddling, Up:= B =
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.