Split Octal (was RE: 8080 Trainer - more info)

From: Jack Peacock <peacock_at_simconv.com>
Date: Wed Apr 22 12:56:17 1998

> > panel monitor used an octal keypad & display, and the octal thinking
carried
> > over to the assembler package. Heath also used "split octal" in the
fashion
> >
> Actually I think Octal is a dumb idea for 8 or 16 bit processors :-) -

A side note...on the IMSAI front panel the address/data switches came in
two colors, red and blue, so you could group them for hex or octal
inputs. (Obscure trivia, the prototype IMSAI used black switches.) You
could tell just by looking at someone's front panel if they preferred
hex or octal. Mine is in hex, S/360 Assembler was the first assembly
language I learned, and it was in hex.

If I recall correctly, Microsoft was an early user of split octal. Soon
after the 4K/8K BASIC, MS came up with an editor/debugger package for
Assembler that used the split octal notation (fuzzy here, does anyone
else remember that package, it was short-lived).

Octal proved useful in suprising ways. On Seymour Cray's CDC 6000
series, with a 60 bit word, you might think that a dump using 15 hex
digits per word would be the most useful, but in fact that was never
done, because the 60 bit word was broken down into 15 and 30 bit
instructions (multiple instructions per word, a Cray innovation I
believe), easy to see in octal but not a good fit in hex. Plus, the
character set normally used was 6 bit, not 7 or 8 bit ANSI.
                Jack Peacock
Received on Wed Apr 22 1998 - 12:56:17 BST