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Compaq Portable 386 Ram Conundrum

arrow_runner

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Mar 7, 2012
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530
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Cincinnati Ohio
I'm working towards getting my Compaq Portable 386 up and running, but found something weird that I don't quite understand.

My system reports 2048kb ram on bootup and for the 'mem' command. It has 4 sticks of 512kb ram installed. According to the jumper settings, it also has 640kb ram onboard.

I had asked an eBay seller to tell me how much ram their Portable 386 had and they said '2688kb' which I thought was a really weird number until I realized that was 2048kb + 640kb.

After thinking about it, I don't remember any 386 or newer systems adding in that extra 640kb, so what's going on here? If my system has it, why doesn't it allow it to be used?

As an aside, if anyone has the 4mb expansion ram cards for sale/trade, please PM me
 
That's common with the Compaq portables of the time. My SLT 286 also has 640KB on the board, and 2MB in expansion cards. You might have to go into the BIOS and enable it.
 
The Portable 386 only has the 2MB fitted into the 4 slots. There is no extra RAM on the motherboard.

The jumpers are for setting how much of the 2MB memory is available to DOS (currently 640K). It's not extra RAM, and the seller was mistaken when they said 2688K.
 
I don't know. I gave the seller pretty clear instructions: "When the computer first turns on, there should be a number on the top left that starts counting. Can you tell me what number it stops at?"
 
Have you opened the back cover at all? Do you know if there are any expansion cards fitted?
 
Yeah I actually had the board out and soldered in a socket where the 40mhz crystal was just to see how overclockable the 386, 387, and Cyrix 486 upgrade chip are. More on that later.

I don't have any of the ram expansion cards, just the 4 simm slots are populated. I forgot to look to see if they are any chips on the motherboard that look like ram chips.
 
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