Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!shadooby!samsung!uunet!dino!ux1.cso.uiuc.edu!uxa.cso.uiuc.edu!jb10320 From: jb10320@uxa.cso.uiuc.edu (Jawaid Bazyar) Newsgroups: comp.sys.apple Subject: Re: RAM chips Message-ID: <1989Dec1.181107.25422@ux1.cso.uiuc.edu> Date: 1 Dec 89 18:11:07 GMT References: <968@madnix.UUCP> <5866@wpi.wpi.edu> <128663@sun.Eng.Sun.COM> Sender: news@ux1.cso.uiuc.edu (News) Reply-To: jb10320@uxa.cso.uiuc.edu (Jawaid Bazyar) Organization: University of Illinois at Urbana-Champaign Lines: 44 In article <128663@sun.Eng.Sun.COM> fiddler%concertina@Sun.COM (Steve Hix) writes: >In article <5866@wpi.wpi.edu>, greyelf@wpi.wpi.edu (Michael J Pender) writes: >> In article <3213@husc6.harvard.edu> huang@husc4.UUCP (Howard Huang) writes: >> > >> >I need to get some more memory for my IIgs, and I have one question: >> > >> > Is it all right to use 120ns chips instead of 150ns in the Apple >> > Memory Card? Can you mix the 120 and 150 chips within the same >> > set of 8? >> I wouldn't mix the 120s and 150s on the same set of 8, the 120s >> would get done before the 150s. > >So? They'll just hang around until the system is ready to read from >them. It's not like they'll be told to do something else before the >access is done. They're just kinda hanging around until then. > Here's a story for ya. I have an Applied Engineering GS-RAM rev. D which had 1meg of 150ns 256k chips on it. It worked fine. I bought a bank of 120ns chips after consulting with AE (they said it would work). It didn't. Most of the 150ns didn't work when I had the 120ns chips installed. After a lot of headaches, I finally got some more 120ns RAM, but in the process I discovered an interesting fact about the GS RAM. You can't mix chips of different speeds in a particular column. Here's a diagram. Column 1 Column 2 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x i.e. Each column must contain chips of the same speed. I imagine the problem is a timing glitch caused by AE's proprietary bank selection logic, the logic that allows DMA access to 6 banks of memory, even though the memory slot only directly supports four banks. If you've got a GS RAM and are going to be adding memory, make sure you buy the same speed you've currently got. Either 150ns or 120ns will work fine. AE recommends 120ns because of all the delay their logic introduces. Apple used 150ns chips on the motherboard. -- Jawaid Bazyar | This message was posted to thousands of machines Junior/Computer Engineering | throughout the entire civilized world. It cost jb10320@uxa.cso.uiuc.edu | the net hundreds, maybe thousands of dollars.