Multipop-68

    An early time-sharing operating system
   developed in Edinburgh by Robin Popplestone and others.  It
   was inspired by MIT' Project MAC, via a "MiniMac" project
   which was aborted when it became obvious that Elliot
   Brothers Ltd. could not supply the necessary disk storage.
   Multipop was highly efficient in its use of machine resources
   to support symbolic programming, and effective - e.g. in
   supporting the development of the Boyer-Moore theorem prover
   and of Burstall and Darlington's transformation work.

   It was not good at supporting the user programs which were
   then the standard fare of computing, e.g. matrix inversion.
   This arose from the fact that while the POP-2 compiler
   generated good code for function call (which is a lot of what
   layered systems like operating systems do) it did not generate
   efficient code for arithmetic or store access, because there
   was no way to police the generation of illegal objects
   statically.  (Hindley-Milner type checking did not exist).
   Indeed, since many OS features like file-access were performed
   by function-call (of a closure) rather than an OS call
   requiring a context switch, POP-2 actually gained
   performance.

   Multipop68 was efficient primarily because the one language,
   POP-2 served all purposes: it was the command language for the
   operating system as well as being the only available
   programming language.  Thus there was no need to swap in
   compilers etc.  All store management was accomplished
   uniformly by the garbage collector, as opposed to having
   store management for the OS and store management for each
   application.

   There was a substantial amount of assembly language in
   Multipop68.  This was primarily for interrupt handling, and it
   is difficult to handle this without a real-time
   garbage-collector.

   [Edited from a posting by Robin Popplestone].

   (1995-03-15)