[TUHS] [TUHS} PDP-11, Unix, octal?

Lars Brinkhoff lars at nocrew.org
Wed Jan 18 16:04:31 AEST 2017


Steve Johnson wrote:
> Historical note: before networking, magnetic tapes were essential for
> backups and moving large quantities of data. Data was stored in
> magnetic dots running across the tape, and typically held a character
> plus a parity bit. Thus, there were 7-track drives for 6-bit machines,
> and 9-track drives for 8-bit machines. But nothing for 9-bit
> machines...

The 36-bit PDP-10 initially used 7-track drives, with six frames to a
word.  During its lifetime sunset, 7-track drives were no longer made,
so 9-track drives were used instead.  The most common encoding was to
store a word in five 8-bit frames, with four bits unused.

The PDP-10 did not have a fixed byte size.  Were there any 9-bit
machines?


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