Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.advocacy Subject: Re: The Amiga's Future Message-ID: <22461@cbmvax.commodore.com> Date: 14 Jun 91 17:18:39 GMT References: <5068@orbit.cts.com> <16647@darkstar.ucsc.edu> <1308@cbmger.UUCP> <28@ryptyde.UUCP> <48@ryptyde.UUCP> <22370@cbmvax.commodore.com> <22414@cbmvax.commodore.com> <55@ryptyde.UUCP> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 29 In article <55@ryptyde.UUCP> dant@ryptyde.UUCP (Daniel Tracy) writes: >Responding to the following: >On the other hand, maybe Motorola missed out on it. More and more new CPUs >are running bus clocks at 1/2 their ALU clock speed. And they're using the >ALU clock speed to stamp the part. If you're targeting people who buy systems >according to clock speed, you win that way." >What's the deal here? I heard that, in the 680x0 line, the chip only runs >at half its clock speed "internally". With a 50MHz 68030, for example, the >chip would only be running at 25MHz. But I also heard that this was fixed >in the 68040. I also read that, at 25MHz, the 040's ALU is running at 50MHz. It doesn't make any sense to say "the chip only runs at half its clock speed internally". A microprocessor is a very complex machine, with lots of different functional units. In any processor, some units may do a new operation every clock cycle, some may take two, three, or four clocks. The 68030 runs at it's rated clock speed, but you have to qualify that. It's minimum bus cycle is 2 clocks, 1.25 if you consider burst. It's cache hits take two clocks, though you can have parallel instruction and data cache hits. I think the small pipeline and ALUs do something new every clock cycle. The 68040 runs pretty much everything, including cache hits, in a single bus clock cycle. It requires a double-speed clock for the ALUs, which do something new twice in a bus cycle. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "This is my mistake. Let me make it good." -R.E.M.