Path: utzoo!attcan!uunet!cbmvax!daveh From: daveh@cbmvax.UUCP (Dave Haynie) Newsgroups: comp.sys.mac Subject: Re: Pierce Explains RISC. was new mac rumors Message-ID: <6107@cbmvax.UUCP> Date: 28 Feb 89 23:39:25 GMT References: <9795@cit-vax.Caltech.Edu> Organization: Commodore Technology, West Chester, PA Lines: 31 in article <9795@cit-vax.Caltech.Edu>, wetter@cit-vax.Caltech.Edu (Pierce T. Wetter) says: >>> For instance the 6502 can do every >>> instruction in one clock cycle, while the 68000 can take up to 70. >> Many 6502 instructions are >1 cycle long, as a glance at any 6502 programming >> manual will quickly confirm. The true speed of any processor is > Ooops, sorry. I meant many 6502 instructions take ~ 1 cycle. I obviously > didn't expect a multiply to run in one cycle. > Pierce Well, no problem, the 6502 doesn't have a multiply instruction. I think there's a little mixing of ideas here. Without wait states, the 6502 takes only 1 clock cycle for each bus access. By contrast, a 68000 takes 4, a 68020 takes 3, and a 68030 takes 2 (the IIx and SE/30 both have wait states). Bus access is only part of it, though. As far as actual instructions go, the 680x0 chips can take 60 or more clock cycles to do a multiply. The 6502's longest instruction takes around 7 clocks, but it's 32 bit multiply routine will undoubtedly take longer at the same clock frequency than the 68030. Perhaps a RISC processor at the same clock frequency can execute one whole reasonable instruction in one cycle, and finish such a multiply faster than the 60 clocks it might take the 68030. The bottom line is who gets the most actual work done in a particular chunk of time. In some cases, it may even be the 6502 that wins (I can think of one case it beats the 68000 at 1/2 the clock speed), but for the most part, don't count on it. -- Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: D-DAVE H BIX: hazy Amiga -- It's not just a job, it's an obsession