Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!pt.cs.cmu.edu!andrew.cmu.edu!cs4w+ From: cs4w+@andrew.cmu.edu (Charles William Swiger) Newsgroups: comp.sys.apple2 Subject: Memory chips, was: Re: BITNET mail follows Message-ID: Date: 3 May 90 05:44:08 GMT References: <9005022007.AA01369@apple.com> Organization: Carnegie Mellon, Pittsburgh, PA Lines: 47 In-Reply-To: <9005022007.AA01369@apple.com> From larrylro@gnh-applesauce.cts.com (Larry LRO): >If you have 120ns chips already installed on the board you probaly should come >as close as possible to the 120ns. The faster the chips the better the >performance. All the ram boards we sell come with 80ns drams installed and our >prices are the best. [ Are they? Glad to hear it. ;-) ] I'm afraid that putting faster RAM chips in a computer will do nothing to make it run faster. Or else I'd be in a long line of //gs owners who're buying 50ns (very fast, but very expensive) chips that would triple the speed of my computer that currently uses150ns both on the motherboard and on the RAM card. The speed of chip refers the time in nanoseconds that the chip requires to perform a memory access. You really don't need chips that run faster than the CPU (and/or the DMA controller) can possibly access them. From what I remember about the timing cycle for memory access in Apple //'s, you have 2/5's of the total time of one (CPU) clock cycle to do the memory access. Working that out shows that you need 143 ns chips to run at 2.8 MHz. Since the chips aren't rated to run quite that fast, ocasionally they'll be forced to cause a wait cycle, which gives them time do finish the access at the cost of taking an extra (CPU) clock cycle. This slows the computer down slightly, so that the apparent speed seems to be somewhere between 2.6 and 2.7 MHz. If you check the manuals, you'll find that Apple claims to run at 2.8MHz only when running in the ROM, for running in RAM they claim a speed of 2.6 MHz. Now then, if you buy 120ns chips, you're guarenteed to not see this problem. And, if you buy 150ns chips, all that means is that the chips work consistantly at 150ns but do not work consistantly at 120ns. There's a good chance that 150ns chips will be able to keep up with the 143ns access time required by the CPU. When I was buying memory, chips were expensive as hell, and the price difference between 150ns and 120ns was $2 a chip. ($64 per MB) Now, you can buy chips much more cheaply (that MB costs $110 instead of $400, and the difference between 150ns and 120ns chips is about $10 per MB). It's worth it to buy 120ns chips now, for the 5% or so speed increase. Of course, all bets are off when you are running a Transwarp or a high speed SCSI/DMA card. Then the faster access time of the 80ns chips will produce a very noticable increase in performance when compared to the slower 150ns chips. -- Charles William Swiger cs4w+@andrew.cmu.edu