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Compaq Portable III and RAM above 640K

V

vbug

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Jan 2, 2021
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Hi everyone, I have an old Compaq Portable III with 640K internal RAM and no RAM extension card. The 640K internal RAM comes from 2*256K SIMM modules + 128 soldered on the motherboard. I found on my closet 2*1MB SIMM modules that seems to work with that Compaq, but it only detects 640K instead of the full capacity. I tried to configure jumpers on the board but I didn't succeeded to get the full RAM capacity. My question : do you know if it is possible to get more than 640K memory without any RAM extension card ? Thanks.
 
I think 286 and 386 Compaq require you to set the ram size in the setup program on the diagnostic floppy, kind of like an IBM AT. I could be wrong though.
 
Hi, thanks for your answer, yes I have that diagnostic floppy and I tried to change things around memory, no results, that's why I was wondering if it is even possible.
 
Been a long time since I used one of those, but I recall when you configure the memory, you have to remove 640kb from the total. So if you have 2mb installed, you would input 1408.

So I was a little off, forgot 128k onboard not 640k since it had 2 256 simms. So input 1920.
 
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Manual has dip switch settings for 1mb simm...So seems 2mb since you have to use pairs. Some sites are claiming 8mb, but that doesnt seem right. But perhaps 4mb simms were not out yet.

Memory Modules Spare Part
256 X 9 SIMM - DISCONTINUED 107380-001
1 MB X 9 SIMM - DISCONTINUED 107379-001


This link says 2048 max.
 
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This is even more confusing, this video is showing it counting 10240kb of memory...o_O Guess thats with the isa/memory expansion unit installed.

 
twolazy said:
Manual has dip switch settings for 1mb simm...So seems 2mb since you have to use pairs. Some sites are claiming 8mb, but that doesnt seem right. But perhaps 4mb simms were not out yet.
Click to expand...

Those dip switch settings are labeled as for "expansion memory", IE, they appear to be for selecting what size modules are installed in the expansion board. (This is bolstered by the "Memory Upgrade Chart" on page five which clearly says "SYSTEM BOARD TOTAL MEMORY: 640K".) The expansion board apparently had three pairs of sockets on it so the total memory's going to be either "2.1MB" if the board is populated with 1.5mb's worth of 256k SIMMs or "6.6 MB" for six 1MB SIMMs.
 
It says max 8mb ram on the expansion unit, then how is he booting 10240k ram in the video? Surely it means it supports 2mb onboard? Definitely confusing.
 
twolazy said:
It says max 8mb ram on the expansion unit, then how is he booting 10240k ram in the video? Surely it means it supports 2mb onboard? Definitely confusing.
Click to expand...

The external expansion chassis connects to a different port on the motherboard than the internal memory expansion card. So if the expansion chassis has an 8MB RAM card in it and the computer has its built-in 640K plus 1.5MB in the form of three 512K SIMMs on the expansion card then the number adds up.
 
Then at the end I assume it is not possible without the expansion card thanks everyone for your contribution :)
 
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