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486 Laptop Memory Identification/upgrade Problem


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#1 mzu

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Posted 04 July 2006 - 03:33 AM

Dear all,
There is a scavenged 486 laptop. I decided to put it to work somehow. It boots up, saying it is "Media Magic PN315/DSTN". BIOS finds 8Mb of memory. Before installing anything it's a good idea to install some more memory. The behemoth has 2 memory slots filled up with 2 strange memory modules.
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What are they? Is it likely I can find an upgrade for them? Where? Or can I find some adaptor to install
regular SIMMs in there?

Google search gives nothing relevant, datasheet on ICs used on those modules says they are 1Mx4. I tried to trace the pinout with a tester - all 59 out of 60 (!) pins are used, the pinout is essentially different from 30 pin SIMM pinout (it has 32 bit data) and different from 72 pin SIMM pinout (there is only 1 RAS, but 4 CASes).

maybe it is a wrong forum to ask, but what do you think are the chances of simply soldering in 72pin SIMM?
Any sugestions?

If someone refers me to another more appropriate forum, I would appreciate it much.

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#2 acklan

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Posted 04 July 2006 - 05:20 AM

What make and model computer is it? Those look like modified SIPP chips.
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#3 mzu

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Posted 05 July 2006 - 11:12 AM

It indeed looks like EDO memory but not exactely SIPP. I found the datasheet on the chip used (424400) and tracked the pinout with a tester. Each
of the modules seem to have 32-bit wide data bus, 4 CAS signals to strobe the column address for each individual byte, and 1 RAS. So it is pretty much like 72pin SIMM, though with only one RAS signal. By the way I checked through JEDEC JESD-21C standard. It lists a lot of wierd memory configs but none with 60 pins on it. So the memory does not conform to JEDEC.
On both memory slots CAS signals different, as well as RASes. All other signals are common to both slots. I just wonder if a bit of soldering will enable me to use a regular 72 pin SIMM in here? Am I understanding correctly, that wiring just one RAS signal to the SIMM will simply allow me to use just half of memory?

AFAIK, SIPP is just a version of 30 pin SIMM with different physical connector (pins instead of blade connector). SIPP was 8 bit, so the memory modules in question are not.

One more question. AFAIR, there was some wierd memory size limit on 486 desktop machines. AFAIR, You were not able to install more then 64MB to a regular MB. Do someone remember what was the cause for this limit, and what was the limiting value.

Thanks in advance

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