bit slice chips (was Re: Harris H800 Computer)

Eric Smith spacewar at
Sat Apr 23 00:12:40 CDT 2016

On Fri, Apr 22, 2016 at 10:03 PM, ben <bfranchuk at> wrote:
>> Not exactly bit-slice, but how about the National IMP-16 chip set?

It's bit-slice. The RALU chips were four bits wide, and were used in
at least three different processor architectures, the IMP-4, IMP-8,
and IMP-16. (Despite the similarity of naming, the actual
architectures aren't very similar.)

The CROM (Control ROM) could be custom microcoded for other architectures.

> Too Early ,

Not too early to be bit-slice. The DEC PDP-6 was implemented as
bit-slice, but not with ICs.

> Too Slow ,

It looks amazingly slow now, but compared to other things available in
1974, it was reasonable.

> Too $$$ is my guess.

Actually it was cheap, again by comparison to contemporary things.

> With out the 6800/6502 8080/Z80 price wars, how much would a 8 bit
> CPU be in the late 70s? $75?

$395 for an 8080 in 1974. Under $20 for most 8-bitters by the end of 1979.

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