Warp wrote:
>   I don't think there's any confusion about that. In a typical RISC
> processor each opcode has exactly the same size, and a fixed amount of
> bits in the opcode are allocated for specified things.

I don't think that's sufficient to make it a RISC processor. That would 
mean both the PDP-11 and the X-560 were RISC processors. The X-560 had 
built-in instructions for COBOL data types, string manipulation (aka 
block moves/compares/character set and case conversions/etc), 
instructions that would do things like push a word on a stack whose 
pointer was in a particular register and set the condition bits to stack 
full/empty/almost full/almost empty, etc. Yet it had 7 bits of opcode, 
one "indirect" bit, four bits of register ID, then either three bits of 
index register and 17 bits of address, or 20 bits of absolute 
(immediate) data. Very straightforward enough that I can still remember 
how the opcodes were laid out after 20 years not using it. Pretty much 
all the microcoded CISC machines were like that, especially those 
expected to be programmed in assembler.

You'd have to talk about addressing modes, pipelines, generalness of 
registers, etc.  Sure, the original RISC processors had a very simple 
model so they could fit more registers, but I think we've gone past that 
now. What you describe might be true of *typical* RISC processors and 
untrue of *typical* CISC processors, but I think everything's complex 
enough now that you need to measure things on multiple dimensions in 
order for it to make any sense.

This one's actually pretty interesting:
http://arstechnica.com/cpu/4q99/risc-cisc/rvc-1.html

(Which has an interesting statistic that might explain why people don't 
code languages for memory efficiency any more: """To help you wrap your 
mind around the situation, consider the fact that in 1977, 1MB of DRAM 
cost about $5,000. By 1994, that price had dropped to under $6 (in 1977 
dollars.""")

-- 
Darren New / San Diego, CA, USA (PST)
  Helpful housekeeping hints:
   Check your feather pillows for holes
    before putting them in the washing machine.

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