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Memory Oddity in IBM PC/AT

lyonadmiral

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I have a PC/AT, 640K base memory.

I have an AST Advantage with 3 megs. If I configure the card to be the only memory card in the system other than the 128k to bump it up to 640k, the memory count gives me 3712k at count up.

I also have an IBM Enhanced Memory Expansion Adapter that also has 3 megs. If I configure the card to be the only memory card in the computer other than the 12k to bump it up to 640k, the memory count also gives me 3712 at count up.

3712 - 640k for each card gives me 3072 expansion memory on each card.

I want to put the cards together. I set the IBM EMEA to start at 640k base. I set the AST to start at 3712k. (Is that an error?) When I power up the memory count only goes to 6400. That doesn't seem right? Shouldn't it count up to 6784k? If I go into SETUP and tell it that there is 6144 in extended memory it gives me the memory size error. I'm trying to figure out the error/problem.

Ideas? I'm probably overlooking something simple.
 
I have an AST Advantage with 3 megs. If I configure the card to be the only memory card in the system other than the 128k to bump it up to 640k, the memory count gives me 3712k at count up.
I also have an IBM Enhanced Memory Expansion Adapter that also has 3 megs. If I configure the card to be the only memory card in the computer other than the 12k to bump it up to 640k, the memory count also gives me 3712 at count up.
3712 - 640k for each card gives me 3072 expansion memory on each card.
Makes sense.
640K + 3072K = 3712K

... other than the 128k ..
Another card, providing conventional memory in the range of 512 KB to 640 KB.

I want to put the cards together. I set the IBM EMEA to start at 640k base. I set the AST to start at 3712k. (Is that an error?)
The 640 KB to 1 MB area is reserved for things like video RAM, ROM, etc.

The first 3 MB card (supplying 3 MB of extended memory) would be set to start its memory at the 1 MB address.
The second 3 MB card (supplying 3 MB of extended memory) would be set to start its memory at the 4 MB address.
The 5170 motherboard's SETUP would be set for 6 MB of extended ('expansion') memory.

An example of two 2 MB cards is shown at [here].
 
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