home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!charon.amdahl.com!pacbell.com!ames!saimiri.primate.wisc.edu!zaphod.mps.ohio-state.edu!wupost!gumby!yale!yale.edu!ira.uka.de!gmd.de!Germany.EU.net!mcsun!chsun!cultnet!cubsfan
- From: cubsfan@cultnet.ch (wrobel)
- Newsgroups: comp.sys.mac.hardware
- Subject: SIMMs on the MAC Classic
- Message-ID: <L4qTTB1w165w@cultnet.ch>
- Date: Fri, 06 Nov 92 15:48:32 GMT
- Organization: CULTNET Communication Systems for Art & Science
- Lines: 55
-
- In comp.sys.mac.hardware I wrote:
-
- >I just popped two 1MB 70ns SIMMs into my Mac Classic, increasing its
- >capacity from 2MB to 4MB. Since then I've had intermittent crashes,
- >usually when doing disk writes, printing, or using the modem. I'm
- >running 6.0.7 and it seems to make no difference whether I use the
- >Finder or the MultiFinder. The About Finder box shows that I have 4MB
- >installed, but something is definitely not right. Is there a way I can
- >test the SIMMs to see if one or both is bad? Is there some kind of
- >incompatibility that I don't know about?
-
-
- Joe.Miles@anu.edu.au replied:
-
- >Hi,
- >I have been down that pathway too ... and after reading the technote 176
- >discovered my errant ways. The Mac Classic will not accept simm
- >modules that are fabricated from 4mbit dies. These 1mbyte simm's have
- >2 (or 3) chips on the simm. These 4mbit dies are connected intenally to
- >appear as 1million addresses of 4 bit wide data.
- >Now the Classic just doesnt quite make the required refresh rate for a
- >given more row (its due to the fact that the memory array is arranged
- >as 2k rows and 1Mbit dies as 1krows). The time taken to cycle through
- >2k addresses is not often enough (I think 3msec) and it becomes
- >forgetful....:(
- >Of course due to instruction/data acesses by the mac some rows will
- >be kept refreshed as a side effect... but sooner or later you will hit
- one
- >that has suffered amnesia and system crash due to incorrect info from
- >memory which usually appears to the user as an address error.
- >
- >Cure: use simms that that consist of 1mbit chips i.e simms that have
- >8 or 9 chips mounted on the module with plusses, se's and classics.
- >Classic II's can handle the simms made with 4mbit dies.
-
- Results:
- Well, I followed Joe's advice and bought SIMMs with 8 chips on them and
- they work perfectly. The SIMMs I had tried earlier had only 3 chips on
- them. So much for the "RAM chips and SIMMs must be rated at 150ns
- RAM access time or faster", which is all the information that the Apple
- documentation provided. The dealer told me the problem was that SIMMs
- for the IBM use a 9th parity bit and the MACs do not, but I think Joe's
- explanation is more to the point.
-
- By the way, in the mean time I found RAM Check, a program from ProVUE
- that tests memory. It gave the new SIMMs a clean bill of health, which
- was confirmed by hours of actual use.
-
- Thanks to Joe and all others who responded.
-
- .......................................................................
- Internet: cubsfan@cultnet.ch
- CULTNET (SWITZERLAND) E.V.
- INTERNATIONAL COMMUNICATION SYSTEMS FOR ART AND SCIENCE
- .......................................................................
-