18 bit CPU; was: Speed now & then
bfranchuk at jetnet.ab.ca
Thu Apr 12 17:16:01 CDT 2018
On 4/12/2018 7:55 AM, Toby Thain via cctalk wrote:
> On 2018-04-12 7:48 AM, Bill Gunshannon via cctalk wrote:
>> On 04/12/2018 02:45 AM, Chuck Guzis via cctalk wrote:
>>> 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" ...
> Apple also used this extension in their Mac C compilers.
>>> (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.
>> Signed 8 bits would be -128 to +127.
> Yes, but Chuck was describing the Univac, where char is a 9-bit type,
> and a signed char is 1 sign bit and 8 magnitude bits, giving +/- 255.
Well I have one better with my cpu, a char is -128 to 384. Bits #8 and
#9 are sign. This way I can use the classic format
<OP><AC><INDEX><OFFSET> for single word addressing.
Are there any FPGA designs out there for the non 8 bit computers,
other than DEC's PDP 7,8,11 and perhaps a PDP 10?
Why in hindsight did I not buy 36 front panel switches?
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