LISP implementations on small machines
cube1 at charter.net
Tue Oct 15 19:25:29 CDT 2019
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.)
More information about the cctech