18 bit CPU; was: Speed now & then

Chuck Guzis cclist at sydex.com
Thu Apr 12 01:45:07 CDT 2018

On 04/11/2018 06:38 PM, Chuck Guzis via cctalk wrote:
> On 04/11/2018 02:48 PM, ben via cctalk wrote:
>> I have a nice 18 bit cpu here, with only a few hardware bugs.
>> Hmm would it work better if I change that around ideas.
>> Care to point to a nice 18 bit version of unix or C.
>> BTW The cpu has a frame pointer S but no S++ --S operations
>> so pushing and popping wild data is not a option.
> Well, the Univac 1100/2200 series mainframes ran V7 Unix--and they're
> 36-bit machines, so probably not far from your 18-bitter--and they're
> ones' complement machines.
> Univac called it "SX1100", so you have a search term.

Remarkably, Unisys keeps a lot of old documentation around.  Here's the
reference manual for their "C" on th 1100:


Looks pretty much like standard C until you get into the minutiae, such
as "A character constant is 1 to 4 characters" and page 4-4 "Data Types"
(9 bit characters and 36 bit ints and 18 bit short ints).

So, it should be pretty straightforward unless you assume that a char is
8 bits, with a signed char having a range of +/-255.


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