Commodore PC-10 - only 512KB RAM visible but 640KB populated

Discussion about old PC hardware.

Commodore PC-10 - only 512KB RAM visible but 640KB populated

Postby Kubik » 2018-2-03 @ 08:59

I was just testing one of the Commodore PC-10's when I noticed that the memory test only recognizes 512KB RAM. I was thinking about populating the remaining 128KB (at least until I finish my RAM card), but to my surprise, the additional 4x64 chips are already populated.
As a total noob when it comes to Commodore PC's, I am puzzled - is this normal? Does the memory test only work with first 512KB? Is there a secret jumper?
I'll be grateful for any hints!
Kubik
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Re: Commodore PC-10 - only 512KB RAM visible but 640KB populated

Postby Nipedley » 2018-2-03 @ 13:37

Have you checked the dip switches as on this website? http://oldcomputer.info/pc/commodore10/#jumper

Apparently switches 3 and 4 control whether 512 or 640KB of ram is used
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Re: Commodore PC-10 - only 512KB RAM visible but 640KB populated

Postby Kubik » 2018-2-05 @ 11:43

Thanks, I vaguely recall seeing that page before. Unfortunately, it didn't help, my PC10-III has totally different mainboard. However, the links lead to some interesting pages where I was able to find something that looks like schematics of my PC10. I didn't have time to analyze them yet, though.
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