Path: utzoo!censor!geac!torsqnt!hybrid!scifi!bywater!uunet!cbmvax!daveh From: daveh@cbmvax.commodore.com (Dave Haynie) Newsgroups: comp.sys.amiga.hardware Subject: Re: Beginer Questions (How Does the amiga use MEMORY?) Keywords: how, beginner, non-techie, etc. Message-ID: <17780@cbmvax.commodore.com> Date: 18 Jan 91 05:56:38 GMT References: <1436@tardis.Tymnet.COM> <762@cbmger.UUCP> Reply-To: daveh@cbmvax.commodore.com (Dave Haynie) Organization: Commodore, West Chester, PA Lines: 69 In article <762@cbmger.UUCP> peterk@cbmger.UUCP (Peter Kittel GERMANY) writes: >In article <1436@tardis.Tymnet.COM> jms@tardis.Tymnet.COM (Joe Smith) writes: >>The term "Fast RAM" applies to both Autoconfig RAM and AddMem RAM. >>The Motorola 68000 CPU can access this RAM without interference from the >>custom chips. >>The term "Slow RAM" applies to both Chip RAM and "C0" RAM. The CPU can only >>access this memory by going through Agnus. If Agnus is busy, the CPU may >>be delayed by several wait states. (Worst case, several hundred wait states.) >We checked this out and verified that immense speed difference. We were just >about to stop shipping, causing big terror in the sales department, when >someone told us what was going on: These new machines had the above explained >slow-fast RAM", and with the speed test programs we used, this resulted in a >speed decrease to the half. So it was not a bug, but normal performance :-( Just to make a point about the system architecture here. With the normal 1.3 Workbench up on the screen, Chip RAM is basically the same speed as Fast RAM (on a 68000 system), assuming no crazy blitter or copper activity is taking place. With just up to two bitplanes in use (or up to four in lores), video fetching takes place entirely during the Chip half of the memory cycle, leaving nearly all the CPU slots for the CPU. There are occasional copper fetches in CPU time, but everything else is during Chip time. Now add a bitplane. All of a sudden, the Chip bus performance, from the CPU's point of view, drops nearly in half, because video fetch is now taking every other CPU cycle (except during horizontal and vertical retrace). Going to four bitplane, or the equivalent, and the CPU only gets into the Chip bus during the retraces, which makes your preformance drop way down there. And of course, available retrace time goes down as you add in overscan. The moral of this story is that the $00C00000 memory will be about as fast as Fast memory in the best case, and real bad in the worst case. If you're doing any kind of four bitplane hires with overscan work, you better have Fast memory or you aren't likely to get any work done. >Morale: If you want to do something good to your Amiga, buy him >some (or much) real Fast RAM and be delighted by the speed gain. And realize that the speed increase isn't just for CPU, but disk and just about anything else as well. Especially with the advent of 3 and 4 bitplane Workbench screens or 2 bitplane VGA-Compatible (productivity) modes with 2.0 and ECS, Fast memory is real important. All Zorro II Fast memory is virtually identical in terms of speed (there may be small differences between vendors, perhaps measurable but insignificant, at least if the designs are any good at all). You don't generally have a choice with 32 bit Fast memory, since for the most part each A2000 Coprocessor board, as well as the A3000 motherboard, has its own 32 bit memory design. It's not all that easy to build the best possible Zorro III memory board, so if such things ever show up, they'll be nearly as different in various performance issues as Zorro II hard disk adaptors are now. Of course, with up to 16MB of built-in 32 bit Fast memory, Zorro III memory boards are much less of an issue. Hardware hackers may be interested in learning that there's a completely working Zorro III memory design documented in the Atlanta DevCon notes. It's not the best possible design, but rather something I cooked up in about a week. But it definitely works, and if you recently upgraded from an A1000 and miss the LUCAS/FRANCES things of that generation, this might be something to look into. >Best regards, Dr. Peter Kittel // E-Mail to \\ Only my personal opinions... >Commodore Frankfurt, Germany \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk -- Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests" {uunet|pyramid|rutgers}!cbmvax!daveh PLINK: hazy BIX: hazy "Don't worry, 'bout a thing. 'Cause every little thing, gonna be alright" -Bob Marley