Intel Corp’s patent for a RISC-like architecture that can accept multiple operating systems and programs with mixed instruction sets reportedly takes pains to distinguish itself from other dual-mode processors such as DEC’s VAX, a processor made in the 1980s that accepted VAX code and its predecessor PDP-11 code, (CI No 3,193). However one reader suggests there is a fair similarity, as far as this one snippet of description goes, to the DEC PDP-12. Its Laboratory Computer Handbook (1971) describes the PDP-12 processor, which can execute instructions from either of two instructions sets, the PDP-8 instruction set and the LINC instruction set. The PDP-8 was arguably the first RISC computer (well before the acronym RISC had been coined), and the LINC instruction set was rather more complex. Interrupts could be taken in either mode. Instructions from both instruction sets could be mixed within a single program or even a single routine; each instruction set offered an instruction for explicitly switching to the other instruction set. Our reader continues I am sure there are many innovations in Merced, but it is always interesting to observe how history repeats when circumstances are suitable.
