[TUHS] mental architecture models, Anyone ever heard of teaching a case study of Initial Unix?

[Douglas McIlroy]

> In order to port VMS to new architectures, DEC/HP/VSI ...
> turned the VAX MACRO assembly language (in which
> some of the VMS operating system was written) into a
> portable implementation language by 'compiling' the
> high-level CISC VAX instructions (and addressing modes)
> into sequences of RISC instructions.

Clem Pease did the same thing to port TMG from IBM 7000-series machines to
the GE  600 series for Multics, circa 1967. Although both architectures had
36-bit words, it was a challenge to adequately emulate IBM's accumulator,
which supported 38-bit sign-magnitude addition, 37-bit twos-complement and
36-bit ones-complement.

Doug
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