Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!van-bc!rsoft!mindlink!a464 From: a464@mindlink.UUCP (Bruce Dawson) Newsgroups: comp.sys.amiga.tech Subject: Re: A2620/30 Message-ID: <933@mindlink.UUCP> Date: 13 Jan 90 21:59:44 GMT Organization: MIND LINK! - British Columbia, Canada Lines: 39 To Bill Seymour's comments on the 2620/30 I would like to add one comment. If you have old (16-bit) fast memory and you buy a co-processor board, the correct thing to do with your old fast memory is to remove it from your Amiga. Throw it out, sell it, anything. If you don't, then everytime you access that memory, your expensive coprocessor board will slow down virtually to the speed of a 7.16Mhz 68000. What a waste! If you need the extra memory (and you may well, if you were used to using all of 3-megs, you should probably expect to upgrade to 5-megs for the '020/'030 because of things like kickstart in RAM, bigger disk buffers so the disks can keep up to the processor etc.) then you should sell your old memory board and buy extra ram for your coprocessor. Your system will run much faster and you will probably make money on the deal. Oh yeah, one other thing. If you haven't already, get a fat-agnus, because otherwise you will have some _really_ slow memory in your memory list. Also, while on the topic of memory speeds, I would like to clear up some misinformation which was tossed around recently. The standard Amiga 68000 cycles last 140ns. However, a 68000 takes four cycles to read or write memory (minimum) so that it actually takes 560ns to read or write anything. Half of this time is spent on the bus, and during the other half, other chips (display chips for instance) can read from the memory. Some memory boards may have wait states, but I'm not aware of any (for the 68000 anyway). After all, it doesn't take very fast memory to run no wait-states at 7Mhz, when it takes four cycles for a read. 150ns memory should work just fine. If there are wait states, then the time will increase to 700ns (assuming one wait state). Many 68000 instructions execution times are determined by the time required to read the instruction. Some take slightly longer, and some, such as multiply (38-70 cycles, plus time) take far longer. Read the manuals for details. The '020 can do three cycle reads, the '030 can do two cycle reads and the '040 can (so I hear) do one cycle reads. Personally, I'm holding out for an '050 that does zero cycle reads :-) So, a stock Amiga can execute a _maximum_ of 7.159/4 million instructions per second or 1.79 million instructions per second. .Bruce Dawson.