Multics

Multics (Multiplexed Information and Computing Service) was an extraordinarily influential early time-sharing operating system.

Retrospective observations

It is more than a little startling to realize that the permanently resident kernel of this powerful multi-processor mainframe computing utility, much derided in its day as being too large and too complex, was a mere 135 Kbytes of code. The first MIT GE-645 had 512K words of memory (2 Mbytes), so the kernel only used a moderate portion of Multics main memory.

Related Topics:
Kbytes - MIT - Mbyte

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Measured another way, the entire system, including not just the operating system, but also the complex PL/I compiler, user commands, and subroutine libraries, consisted of about 1500 total source modules. These averaged roughly 200 lines of source code each, and compiled to produce a total of roughly 4.5 Mbytes of procedure code, which though small today was fairly large by the standards of the day.

Related Topics:
Compile - Mbyte

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Multics compilers generally optimised more for code density than CPU performance, for example using small sub-routines called operators for short standard code-sequences, making direct comparison of object code size with more modern systems less useful. High code density was a good optimisation choice for a multi-user system with expensive main memory, such as Multics.

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