17 Apr
2006
17 Apr
'06
11:14 a.m.
Does anyone remember the conflict between the MITS and
IMSAI (actually, the
rest of the world) about using octal vs. hex representations of data? It's
very obvious just by looking at the two systems--the Altair 8800 spaces the
front panel toggles in groups of 3, whereas the IMSAI 8080 color-codes the
switches in groups of 4. I think that the early MITS assembler used octal,
although it's very hard to remember.
Yes - one of the things I didn't like so much about the Altair - I came from an
IBM mainframe background and HEX was "in my blood" (I still find myself
going 8, 9, 10, A, B, ... oh crap ...) when I am counting things (not computer
related) sometimes.
To be fair to MITS however - note that the Intel 8080 processor was deisgned
for octal - the register fields are three bits an on octal boundaries, as are the
condition bits and restart vectors - most of the instruction set was originally
documented in octal - I think Ed and gang just did "what seemed to make
sense at the time".
More than one Altair owner disagreed - I never modified my machine, but
just got used to "seeing the switches in groups of four" - At least a couple
of the photos I've seen on the net have lines drawn on the front panel to
separate the groups of four. Another Altair 8800 that I picked up later has
what I think is a really elegant solution. The owner simply used some of the
little plastic colored toggle switch lever covers to mark the second bank of
four switches from the right - makes it easy to see them in hex, and does
not permanently alter the machine.
And ... apparently some IMSAI owners also disagreed! - One of my
IMSAI front panels has the switch colors arranged in groups of three
(which points out a nice feature of the IMSAI kit - you could built it
either way).
Dave
--
dave06a (at) Dave Dunfield
dunfield (dot) Firmware development services & tools: www.dunfield.com
com Collector of vintage computing equipment:
http://www.parse.com/~ddunfield/museum/index.html