Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: Motorola vs Intel (who's faster?) Keywords: Amiga runs at 3.5 MHZ? Message-ID: <13229@cbmvax.commodore.com> Date: 16 Jul 90 17:54:04 GMT References: <1990Jul10.055108.22796@agate.berkeley.edu> Reply-To: daveh@cbmvax (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 53 In article <1990Jul10.055108.22796@agate.berkeley.edu> joechung@sandstorm.Berkeley.EDU (Joeseph Chung) writes: >A friend of mine said the other day that Motorola rates its CPU's twice as >fast. So in effect, my Amiga's running at a little over 3.5 MHZ. Your friend is on the right track, but obviously confused about the details. Basically, it's meaningless to compare the clock speeds of different chip architectures without knowing both architectures. The clock speed has little to do with how long the actual chip takes to perform an operation. For at least older CPUs, one actually meaningful number is the bus speed -- how many clocks does the CPU take to run a single cycle on its memory bus. A 68000, an 8086, and several other CPUs of the same vintage take 4 processor clock cycles to run one memory cycle. The Z-80 runs a 3 clock cycle to fetch an instruction, a 4 clock cycle to fetch data. The 6502 takes a single clock for its minimum memory cycle. So while you can figure that an 8MHz 68000 and 8MHz 8086 talk to memory at about the same speed, an 8MHz 6502, if such a chip existed, would be talking to memory more like a 32MHz 68000. >One of the reason he sights is that: Motorola & Intel are about the same >level in technology, and yet Motorola has come out with a 50MHZ chip already >while Intel is still around 33MHZ. Therefore, the actual speed of the >Motorola chips are 1/2 what the manufacturer says. He's pretty confused here. Motorola and Intel chips of the same basic generation are going about the same memory speed at the same clock rate. For example, both the 80386 and the 68030 take two clock cycles to access memory. Motorola is indeed making faster 68030s than Intel makes 80386s, and they really do go faster. Some RISC chips actually handle one memory cycle per clock cycle, and the burst mode found on 68030s, 68040s, and 80486s lets these chips fetch 4 longwords in as little as 5 clocks, coming close to 1 word per clock. And memory fetch is only part of the question. Many CPU operations are internal to the part, and some happen in fewer clocks. The 68040, for instance, takes only one clock to fetch from internal cache, while the 68030 takes the standard two clocks for internal cache fetches (both can fetch from both caches at the same time). >No flames please. I just want to know if what he said is true. I'm a little >surprised the hear that my 68000 actually runs at 3.5 compared to an Intel. To sum up, an 8MHz 68000 runs much the same kind of cycle as an 8MHz 8086. An 8MHz 68020 can hit memory 1.5 times as fast, an 8MHz 68030 or 80386 can hit memory 2 times as fast, and a 8MHz 68030 or similar chip can hit burst mode memory nearly 4 times as fast as the 68000 or 8086. Of course, since the 68030 has a 32 bit bus, this is actually a data transfer rate closer to 8 times faster. >-jc -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "I have been given the freedom to do as I see fit" -REM