LISP implementations on small machines

[Paul Koning]

> 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.

	paul