PDP-6

The PDP-6 (Programmed Data Processor-6) was a computer model developed by Digital Equipment Corporation (DEC) in 1963. It was influential primarily as the prototype (effectively) for the later PDP-10; the instruction sets of the two machines are almost identical.

Architecture

The PDP-6 was DEC's first "big" machine. It used 36-bit words, in common with other large computers at the time from companies like IBM, Honeywell and General Electric. Addressing remained 18-bit, as in earlier DEC machines, allowing for a 256 kword main memory. Memory was implemented using magnetic cores; a typical system included 32,768 words (equivalent to 144kB on modern machines).

The instruction set architecture could be categorized as "one-and-a-half address"; instructions contained one full 18-bit memory address, and a second four-bit address that could specify one of the first sixteen memory locations as an "accumulator" or "AC". Another four-bit field in the instruction allowed for any AC other than AC0 to be used as an index register.