Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: Question about the difference between A3000-16/50 and A3000-25/50 Keywords: A3000 speed Message-ID: <21306@cbmvax.commodore.com> Date: 6 May 91 21:26:54 GMT References: <116684@tut.cis.ohio-state.edu> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 32 In article metahawk@itsgw.rpi.edu (Wayne G Rigby) writes: >In article <116684@tut.cis.ohio-state.edu> erd@giza.cis.ohio-state.edu (Ethan R Dicks) writes: >>In short: if I buy a 3000-16/50, will any future '040 run at a higher speed? >>If I intend to run a 25 Mhz '040, will I need an A3000-25/50? I am aware of >>RAM speeds and can select any FAST RAM to be of the appropriate speed for >>either 16 or 25 Mhz. >If you got an '040 board, the board would basically take over the bus and >run at its own clock speed. So if you got, for example, a 70 MHz 68070 >accelerator board, your computer would run at 70 MHz, and your 16 MHz >68030/68881 or 25 MHz 68030/68882 would be disabled for all intents and >purposes. Not quite. The A3000 motherboard can be run at either 16MHz or 25MHz. Period. Some come with a 16MHz 68030 and 68881, which wouldn't work at 25MHz. So the motherboard gets a 16MHz clock, thus keeping the 68030/68881 happy. Just like in the A2000, a coprocessor card can have any processor running at any speed it likes. However, when that card talks to the A3000 motherboard, it must look like a 16MHz 68030 if the A3000 is set for 16MHz, a 25MHz 68030 if the A3000 is set for 25MHz. Since it was obvious early on that some coprocessor boards might NEED, depending on design, to run synchronously to the A3000 motherboard, and thus supply their own clock, we made it possible for a designer to let this happen. So it's possible for a coprocessor board (68040, whatever) to run the A3000 motherboard at 25MHz, even if it came stuffed for 16MHz operation. However, in such a cranked up system, the original 16MHz 680x0 chips will have to stay shut down. -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "That's me in the corner, that's me in the spotlight" -R.E.M.