The "cent key"

[Ric Werme]

Jerry Feldman wrote:
On Sun, 08 Jul 2007 11:36:02 -0400

> The ASCII character set was originally a 7 bit character set defined in
> the late 1950s when the input device was an ASR 33 teletype. ASCII
> started to replace the old baudot code which was (if I remember a 4 bit
> code).

Five bit code, see
http://www.baudot.net/
http://www.science.uva.nl/faculteit/museum/papertape.html

OBtW:  I worked as a contractor at a place from time to time and one of the
young 'uns tried to impress his coworkers with the following:

  Core memory always used odd parity because reading core memory caused the
  data to be zeroed.  That way odd parity tests would catch the read and
  forgot-to-write cycle.

  Why does RS232 data generally use even parity?

I looked up (I was the only one working at the time), looked straight at
him, and said "Paper tape."

He was crestfallen, the others were merely confused.

The reason, obvious to anyone who has had to prepare a paper tape offline,
is that if you made a mistake, you backed up the tape, and pressed the
rubout key.  On ASCII teletypes, that punched all 8 holes, and programs
that would read the tape would discard rubouts.  Even parity allowed
rubouts to pass the parity test.

    -Ric Werme

P.S. "The only thing worse than fan-fold paper tape is non-fan-fold paper
tape.  - Bob Clements