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@classiccmp.org> >> wrote: >> >> >> >>> On Oct 3, 2019, at 12:39 PM, Chuck Guzis via cctalk <cctalk@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
