Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!cbmehq!cbmger!peterk From: peterk@cbmger.UUCP (Peter Kittel GERMANY) Newsgroups: comp.sys.amiga.hardware Subject: Re: Beginer Questions (How Does the amiga use MEMORY?) Keywords: how, beginner, non-techie, etc. Message-ID: <762@cbmger.UUCP> Date: 17 Jan 91 14:03:46 GMT References: <1436@tardis.Tymnet.COM> Reply-To: peterk@cbmger.UUCP (Peter Kittel GERMANY) Organization: Commodore Bueromaschinen GmbH, West Germany Lines: 41 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.) > >>What's so important about "Fastmemfirst" ? Does it prevent the >>using up of "CHIP" befor "Other" memory is full? How does it do it? > >Here's where "C0" RAM comes in. Older A2000's and A500's with the A501 >memory expansion have 1 meg of memory connected to Agnus. The first 512K >is Chip RAM, where Agnus can do DMA (Direct Memory Access) to drive the >video display and sound channels. The second 512K is also connected to >Agnus, but the DMA channels can't access it. This second 512K has been >called "Slow-Fast RAM"; "Slow" because the 68000 CPU has to go through >Agnus to get to it, "Fast" because it can't be used like Chip RAM. Well, obviously time to tell another anecdote from the old days. You know we in Germany had first the A2000-A which differed from the later B version in that the second 512 K RAM resided on an own little expansion board sitting in the CPU slot. And yes, this was *real* Fast RAM. Now, then came the new A2000-B models. After a few days we got complaints from dealers and customers that there was something wrong with these machines: They were only half as fast as the old ones! Something was totally wrong! 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 :-( 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. -- Best regards, Dr. Peter Kittel // E-Mail to \\ Only my personal opinions... Commodore Frankfurt, Germany \X/ {uunet|pyramid|rutgers}!cbmvax!cbmger!peterk