Arthur Krewat krewat at kilonet.net
Tue Sep 19 02:42:02 AEST 2017

The MACRO-10 assembler used a keyword ASCIIZ to store that 
7-bit/1-bit-wasted ASCII format.

MOVEI 0,[ASCIIZ /Hello there

for example. It was the defacto standard for null-terminated ASCII strings.

When I later moved to C on 8/16-bit computers, I remember thinking 
"what's with this signed 8-bit char thing?" ;)

There was also SIXBIT - almost everything ASCII had, but only upper 
case. The filesystem used that for filenames and extensions, and it was 
used in a few other areas. So any library calls like open() would have 
had to convert the ASCII filename to SIXBIT before doing any monitor calls.

On 9/18/2017 9:50 AM, Clem Cole wrote:
> On Sun, Sep 17, 2017 at 11:22 AM, Arthur Krewat <krewat at kilonet.net 
> <mailto:krewat at kilonet.net>> wrote:
>     I have a C compiler for TOPS-10 that I got off the Internet back
>     in 1988. Still haven't messed around with it enough to get it to
>     run, but ...
> ​There was a PDP-10 C compiler in the late 1970s, that was kicking 
> around CMU, MIT and Stanford which we used to write backup10 and ​and 
> an implementation of tar.   IIRC, it was based on the the Ritchie 
> front end and was V6 in syntax (i.e. pre-V7 or typesetter C - aka 
> 'White Book).   I've forgotten the rules of chars, but I remember you 
> had to be careful.   I think it was 4 9-bit chars to transfer things 
> (4*9=36 bits), but I think I remember there were cases on output that 
> it wanted to wash it through a 7-bit PDP-10 char (5*7+1 =36bits) which 
> was the 'norm' for most languages like SAIL, BLISS et al.
> I did not mess with much, but that time, I was transitioning from the 
> 10's to UNIX by that time.   I added support for the -20's dumper 
> tapes to backup10 which were almost but not quite the same.  But that 
> was the last I messed with it. Mike Accetta and Fil Aliva (of CMU Mach 
> fame) I remember had their had in that subsystem, at one point.  And 
> of course Danny Klein is always a good one from those days to ask too. 
> I'll see if I can dig them up and ask.

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