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Memory upgrade problems

Posted on 1997-10-04
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Last Modified: 2013-11-10
Hello,

I just purchased 4 additional SIMM 4 Mb 30-pin memory to my 486 computer. I previously had 16 Mb installed (4x4 Mb SIMM).

When I had installed them the BIOS found all 32 Mbytes.
Though, during booting Windows95 the computer restarts after few seconds. I also tried using Windows NT, but this failed in the same mannor.

I was able to get the computer to boot MS-DOS without loading EMM386.EXE. Thereafter I used a test program from AMI called AMIDIAG to see if it could detect any problems.

This program failed at the cache memory test. It counts up from 0 Mb to 16 Mb (0ffffffh) without any problems. At the address 1000000h it reboots without any notice.

1) I tested with different memory cards for the upper 16 Mb    memory.

2) I tried switching to an identical motherboard.

3) I changed the video card from an accelerator card to an    old TsengLab.

4) I tried with all add-on cards but the TsengLab video card    and the floppy disk controller removed.

All these actions did not solve the problem.

Now I changed some parameters in the BIOS settings.
When disabling the cache memory for the upper 16 Mbytes the computer was able to boot both Windows95 and Windows NT, though it was slower than it was with the *old* configuration :).

This is the status of the problem today.

The hardware:

Motherboards:   80486 CAM/33-U0 (M418U00) and 80486                 CAM/50-U0 (M41AU00)
                (Both specified to handle up to 32 Mb RAM)

Chipset:        82C206, 82C481A and 82C482AF

Cache:          256kb 8 pcs 32k x 8 chip SRAM (Type:dt71256                       S25TP)
                      3 pcs 16k x 4 chip Tag RAM                       (Type:WS22B65AK-15)

BIOS:           AMI 40-0100-B81105-00101111-070791-UMC480A-F                 (date 03/16/1992)

Questions:

Q1.     Does anyone recognize who the motherboard         manufacturer is?

Q2.     What settings in the BIOS should be changed to make         the computer able to run properly without disabling         the cache memory for the upper 16 Mbytes of memory?

Q3.     Do I really have 256k cache memory? My BIOS detects         256k and the motherboard is strapped for 256k cache.

Thanks for any answers!!
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Question by:discus
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evil_ed earned 150 total points
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Hi Discus ...

Here are some answers for you :

1 nope, but doesn't matter since the problem is not motherboard
  related but more an architectural problem.

2 not possible it is a hardware problem not a settings problem

3 yes as far as i can determine with the specified number of   chips and their typenumbers.

4. uhh there was no 4 , yeah but you'd like to know which hardware problem i'm talking about right ??

Okay due to the fact that most of the older system which were developed on plain ISA bus architecture mainboards that have ISA
on it will not support more than 16 megabytes memory (at least really support.
Unless you use only PCI or EISA cards that are dma capable your system will lock up in all kind of ways simply because dma transfers will be placed on wrong memory locations.
If you don't have any ISA cards with dma this is a different story but my guess is that there is a Network card or a Disk controller that is capable of doing DMA transfers.
For example OS/2 is able to use the memory above 16 mb , but doesn't report it since it is turned into a swapdrive kinda memory pool.

so i wish you all the best and can only tell you that for me the solution was to get rid of my DMA scsi controller and replace it with a cheaper version which doesn't support DMA

Kind Regards Eddie
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