LISP implementations on small machines

[Jay Jaeger]

On 10/3/2019 1:04 PM, Guy Sotomayor Jr via cctalk wrote:
> 
> 
>> On Oct 3, 2019, at 10:26 AM, Paul Koning via cctalk <cctalk at classiccmp.org> wrote:
>>
>>
>>
>>> On Oct 3, 2019, at 12:39 PM, Chuck Guzis via cctalk <cctalk at classiccmp.org> wrote:
>>>
>>> On 10/3/19 9:01 AM, Noel Chiappa via cctalk wrote:
>>>
>>>> The PDP-6 and KA10 (basically a re-implementation of the PDP-6 architecture)
>>>> both had cheapo versions where addresses 0-15 were in main memory, but also
>>>> had an option for real registers, e.g. in the PDP-6: "The Type 162 Fast
>>>> Memory Module contains 16 words with a 0.4 usecond cycle." The KA10 has
>>>> a similar "fast memory option".
>>>
>>> A bit more contemporary example might be the low-end PIC
>>> microcontrollers (e.g. the 12F series).   Harvard architecture (14 bit
>>> instructions, 8 bit data), but data is variously described as
>>> "registers" (when used an instruction operand) or "memory" when
>>> addressed indirectly.   That is, the 64 bytes of SRAM can be referred to
>>> as either a memory location or as a register operand.
>>
>> Then again, the PDP-10 has that "two ways to refer to it" as well.  In that case, you do have dedicated register logic, and what happens is that memory addresses 0-15 are instead redirected to the register array.  The same applies to the EL-X8.  The way you can address things doesn't necessarily tell you what sort of storage mechanism is used for it.
>>
> 
> So does the PDP-11.  The 8 registers are mapped to the top 8 words of memory so you can do some quite interesting things.  It is also possible to run a (small) program in only the registers (e.g. no memory at all).
> 
> TTFN - Guy
> 
> 

FYI, not ALL PDP-11 implementations can do this.  In particular, the J11
(used in PDP-11/73 and others) does not map the registers into memory
locations.  I suspect, but have not verified, that any PDP-11 processor
with multiple register sets (e.g., one for user one for kernel, etc.)
are likely to behave this way.

(One on one reply since the message was quite old.)

JRJ