Multipop-68

operating system 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 ElliotBrothers 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)