Chad Price price at helios.unl.edu
Mon Feb 22 11:29:17 EST 1993

Ken Baker ("bakerk at frir.afrc.ac.uk") writes:

(in discussing the DEC VMS operating system)

>> 1] More flexible
>> 2] Smaller instruction set makes it faster

As a computer person faced with supporting GCG (on an as-yet unknown platform),
I've  followed this with some interest.

With some few exceptions, it doesn't matter which operating system you select
(as long as its a real multi-tasking operating system, rather than an imitation
like MS Winodws). Some things are easier in some that in others, and some are
limited to proprietary hardware. But the technical abilities of most modern
operating systems are quite similar, and other factors become the reason for
choosing one over another.

I'd like to point out that "instruction set size" has no direct bearing on
which operating system runs on it, or how fast that operating system runs. It
is solely a feature of the hardware on which the OS runs.  Modern RISC-oriented
processors tend to run any operating system faster than the equivalent CISC

RISC = Reduced Instruction Set Processor
CISC = Complex Instruction Set Processor.

RISC is characterized by a number of technical features having to do with that
number of instructions hard-wired (built into) the processor, the method by
which the instruction set allows the processor to interact with RAM (memory),
and the number of processor cycles it takes to run a single instruction
(depending on the amount of parallelism built in, more than 1 instruction may
be processed in a single instruction cycle). Because the instruction set on a
RISC machine is entirely hard-wired into the processor (not micro-coded - see
below), any individual instruction can be expected to run faster. The trade-off
is that it often takes more instructions to accomplish the same task. The
general consensus seems to be that despite the greater number of instructions
to accomplish a given task, the RIC machine can accomplish things faster than a
CISC machine. But note that the Intel 486 chips (a CISC chip) approach the
speed of similar-age RISC chips. The DEC Alpha is a newer generation (RISC)
chip and seems to be about the fastest thing on the market (this month).

CISC has far more instructions available, mostly implemented by something
called microcode, which is a program built into the processor. Many of the
originally RISC characteristics are now showing up in CISC processors (except
of course, large reductions in the number of instructions).

>> 3] Supports a graphical user interface

	Most operating systems do this now, its a matter of writing a program
to support the GUI (including VMS and all UNIX flavors).

my $0.02 about OS's and hardware.

price at helios.unl.edu
cprice at molecular.unmc.edu

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