[TUHS] Why did PDPs become so popular?

Paul Winalski paul.winalski at gmail.com
Sat Dec 30 12:20:09 AEST 2017


On 12/29/17, Kevin Bowling <kevin.bowling at kev009.com> wrote:
> Enlightening to read
> about how the coherence protocol was developed in software.  How was
> the ISA, and I assume even implementation detail, kept equal or close
> enough to the eventual microprocessor parts?  Does the "Privileged
> Architecture Library" mean it was effectively microcoded?

Yes, IMO the Alpha PALcode was a form of microcode.  DEC designed the
Alpha ISA with the hardware folks working closely with the VMS and DEC
UNIX (soon to become Tru64 UNIX) OS groups to insure that the correct
balance of PALcode vs. implemented-in-hardware was struck.

-Paul W.


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