On 31 Jan 99, at 5:05, Bob Chapel wrote:

> Can anyone tell me if UNIX will run on any RISC processor or does it
> require a specific type of a RISC chip?  I recall apple using RISC
> processors and wonder if UNIX can be loaded to an apple for this
> reason.

  Apple's AUX (A/UX) was a version of Unix for their 68000-family Macs.
It's barely possible that it might run (but not quickly...) on the 68K
emulation in their PPC machines.

> Can anyone direct me to some info re: RISC processors .  Given their
> reduced instruction set do they require substantially fewer cycles
> to complete their tasks such that say a 50mhz chip would be the
> equivalent of perhaps a 100mhz INTEL.....stated more
> succinctly....How does one rate the power of a RISC chip relative to
> an INTEL compatible.

  Actually, its the other way around.  Because a RISC CPU implements
fewer instructions, they have to be only the simplest and most basic.
On average, that means one RISC instruction accomplishes only part of
what a CISC instruction might have.  The benefit is that simple
instructions make the CPU, over all, easier to speed up, to more than
compensate for the less-capable instructions.
  So in theory, a 300 MHz RISC CPU might perform about like a 200 MHz
CISC CPU -- but aside from economies of scale, only cost as much to
make as a 150 MHz CISC model.
  In overclocker terms, the simplified RISC CPU produces less heat as
it operates, allowing it to run at a higher clock frequency.

  If CPUs were like flavours of soda pop, CISC would be like "cola" and
RISC like "citrus".  But it still matters whether we're talking Coke or
Pepsi, 7-Up or Mountain Dew.  Every different family of RISC processors
is still a different processor family, with its own set or registers
and instruction codes.  They happen to embody the RISC *design
concept*, but concepts don't execute programs.
  To go back to your first question above:  There are flavours of Unix
for a lot of different CPUs, some RISC and some not.  There is
*probably* at least one version for the particular RISC CPU you have in
mind; there's no such thing as a program binary that "will run on any
RISC processor".

David G

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