[ntp:questions] Local (own site) NTP servers.
oberman at es.net
Wed Jul 29 05:11:11 UTC 2009
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> David Woolley wrote:
> > Richard B. Gilbert wrote:
> >> ISTR reading that the Intel 80x86 line was CISC on top and RISC
> >> underneath. I couldn't swear to it though. All I ever saw or worked
> >> with was the CISC part of it.
> > I think that pretty much defines CISC. CISC machines are normally
> > micro-program driven machines.
> They didn't used to be. However, with the VAX 8600, for example, the
> instruction set was implemented in microcode. So were the diagnostics
> for that matter.
True. but that was before the time of most of the readers here. Most CISC processors after about 1972 were micro-engine based. the original PDP-11 was not, but it was soon re-engineered as the PDP-11/20 with a micro-coded processor. The PDP-11 was the last non-micro-coded system from Digital. IBM went to micro-coded systems for their main-frames about the same time as did most others.
So, while CISC could be done without a micro-engine, it was onlhy the earliest of the CISC mechines that did so. All VAX systems had micro-engines including the origianl 11/780 and 11/750.
Most systems before the late 60's were effectively RISC, although no one called them that. The PDP-8 instruction set was 8 basic commands, AND, TAD, ISZ, DCA, JMS, JMP, IOP, and OPR. The OPR instructions were, effectively, a micro-engine of 19 slightly more complex instructions, but all were implemented in very simple DTL logic and none took more than a single cycle and the full 27 insgtructions were simpler than most RISC processors.
R. Kevin Oberman, Network Engineer
Energy Sciences Network (ESnet)
Ernest O. Lawrence Berkeley National Laboratory (Berkeley Lab)
E-mail: oberman at es.net Phone: +1 510 486-8634
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