[TUHS] 6-bit, 7-bit and 9-bit byte UNIXes

Norman Wilson norman at nose.cs.utoronto.ca
Fri Oct 1 10:47:22 AEST 2004

The very first UNIX ran on the PDP-7, which had 18-bit words.

I happen to have the assembly-language source code to parts
of that system.  Many programs contain error-handling code
that does something like this:

	lac d1
	sys write; 1f; 1
	jmp somewhere

1:	077012


d1:	1

Evidently the system thought in words in those days
(the second argument to sys write is presumably a word
count), but the single word written is a strong clue
that 9-bit bytes were used, and that a certain concise
error message that people love to complain about was
there from the beginning (and why not?).

Norman Wilson
Toronto ON

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