Re: a bit of history, Stealing a Great Idea from the 6600

According to Scott Lurndal <slp53@pacbell.net>:

mitchalsup@aol.com (MitchAlsup1) writes:

Maybe now with 4-or-5-bit condition codes yes,
But the early machines (360) with 2-bit codes were already constricted.

>
The B3500 (contemporaneous with 360) had COMS toggles (2 bits) and OVERFLOW toggle (1 bit).

As far as I can tell, the 360 was the only machine with short encoded
condition codes.

In their archtecture book Brooks and Blaauw say it was a mistake, but
it also would have been a problem to fit conditional branches into the
instruction set if they needed more instruction bits to say which
codes to test. As it was, the branch instructions had 4 condition bits
which let them check for any combination of two-bit conditions along
with 1111 for unconditional branch and 0000 for no-op.

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