Is RISC faster

[Charles Hedrick]

I'm always wary of acronym games.  Only marketeers like them.  You get
speed when the instructions that you use most run fast.  There are several
ways to do this.  RISC is one approach.  In its pure form (and most
commercial RISC systems are not pure) it simplifies the instruction set
(particularly addressing modes) so that all instructions that can be made
to work in a single cycle.  Thus some CISC instructions end up being
replaced by several RISC instructions.  The reason it works out is that
normally you don't really need to use all those fancy instructions and
addressing modes.  That is, on average you don't really have to use 3 RISC
instructions for every CISC instruction.  In effect RISC wins because the
CISC machine has to have extra complexity to handle fancy cases that
aren't really needed in practice.  However there are other approaches to
going fast.  We're starting to see chips that implement more traditional
instruction sets, but make the common instructions execute in one cycle.
Final results still depend upon the quality of design and execution -- as
well as the compilers available for them -- at least as much as on things
such as RISC vs. CISC.  I think it's very interesting to know the
approaches adopted by various designs, but I certainly wouldn't buy or not
buy a product because it was RISC.