Re: [TUHS] Encoding an ISA: Random Logic vs. Control Stores

There seems to be confusion here about microcoding vs. discrete logic/LSI. All but the initial 11/20 (and its variants) are microcoded. That is there is a programmed sequence of operations in the execution of the individual instructions. The less popular 11/60 even featrued a writable control store. All of the early PDP-11s were built out of discrete logic. Relatively simplistic combinations of various logic chips, gates, flip flops, etc.. A lot of these were encapsulated into the DEC "Flip Chips" small circuit boards to do common sets of operations. While this is by modern standards, crude, it doesn't preclude microcoding and other advanced tasks. I worked on a supercomputer built that way (Denelcor HEP built largely out of Motorola 10800-series ECL chips). As I previously stated, the 11/44 was the last of the discrete logic PDP's in 1979. The later systems were all large scale integrated circuit based. First starting with the LSI-11/03 on the Q bus, quickly followed by the 11/23 and the Unibus 11/24.