29 Oct
2010
29 Oct
'10
9:55 a.m.
From: Johnny Billquist <bqt at softjar.se>
I have not seen anyone comment any of the other things I listed as
possible firsts on the PDP-11.
Can anyone come up with an earlier machine that used condition codes?
The ICT 1301 had up to 100 'indicators' specified by two BCD digits in the
instruction. All could be tested with an unconditional jump and some could be set and
unset by program too. Number zero was always on to give an unconditional jump. There were
ones for equal, greater and less as well as overflow, parity error, front panel switch
states, as well as various peripheral statuses. Does that count?
How about general registers with addressing modes,
which is totally
orthogonal? How about having the PC as a general register?
Not quite the same thing but IIRC the Elliott 920A used core location zero as its program
counter. To be more accurate it used 0 by default when not using interrupts. When using
interrupts it used 0 for level 1, 2 for level 2, 4 for level 3 and 6 for base level code.
It also used those addresses plus one for its modifier (B) register. This speeded up
interrupt processing as no need to save those registers.