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386 board that takes 64mb ram?

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First post, by cyberluke

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Hi, I bought 4x16mb simm 30pin modules on ebay. Normally, they are probably for some old Mac. I know you need to fill at least 4 slots of 8 in 386 with the same module. Putting this in my board show up only 16mb, not 64mb. And after a minute the computer freeze no matter if you boot already or still in bios. Sometimes it showed garbled characters.

Now Im back at 8x1mb, all slots are full and I have 8mb ram. I would like to have more in order to run Windows 95 on this machine. It is a bit clumsy and explorer.exe will crash after updating to osr2 because it requires at least 12mb memory.

Is there some bios hack for boards that have ram limit or can you recommend a 386 board that would take more memory? Thank you!

Reply 1 of 27, by GigAHerZ

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Maybe your board has not implemented/put down a trace on the last address line? Then it would never support the 16MB modules.

I myself am rocking 8x4MB modules giving me 32MB total for my 386.

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 2 of 27, by cyberluke

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I need to google what that means. So 8x8mb modules could work or 8x4mb modules? The cpu is 386dx-40 onboard soldered plus I added IIC 4c87-40 floating point unit coprocessor. I read that only 386sx have stripped down architecture and allow only 16mb ram total.

Reply 3 of 27, by cyberluke

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It seems the board does not support it, but it will show up 16mb if I put 4x16mb. So I think it can read the module, just cannot load all of them. If I put 2x16, it wont start at all.

Reply 5 of 27, by GigAHerZ

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cyberluke wrote on 2021-10-13, 09:41:

So 8x8mb modules could work or 8x4mb modules?

There are no 8MB modules. 30pin SIMMs go in the multiples of 4, not 2. So you have 256kB, 1MB, 4MB, 16MB.

cyberluke wrote on 2021-10-13, 09:44:

...but it will show up 16mb if I put 4x16mb...

Well, that kind of indicates that it reads the modules to be 4MB in size.

cyberluke wrote on 2021-10-13, 10:34:

What motherboard you have, please? I have some KMC board with AMI bios.

I'm mainly running M-321 board.

"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!

Reply 6 of 27, by konc

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Just to rule out this scenario, are you sure that the modules you bought are 16MB? I mean not because the seller said so but after confirming the capacity from the chips or trying them on another board.
Not that it's unlikely for a 386 board to only recognize up to 4MB modules, 16MB ones were exotic stuff back then.

Reply 8 of 27, by imi

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are there jumpers on the board for memory size?

could also be, that the board simply isn't compatible with your memory, posting more info/pictures of what board and memory you're using exactly could help.

Reply 11 of 27, by maxtherabbit

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16MB 30-pin SIMMs are pretty uncommon. I have never even seen one in person and I've been working with this stuff since it was commercially relevant. I'd forget about using them and get yourself some 4MB sticks

Reply 14 of 27, by cyberluke

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Jumpers will be similar to this, so 16mb is maximum. 4mb modules can fit only half of the slots: https://stason.org/TULARC/pc/motherboards/U/U … MC-OPTI291.html ...so I need to find a jumper settings for 386 board that mentions 32mb and then buy that board. I think PC Chips were quite good.

Reply 16 of 27, by imi

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if you want a 386 board with more RAM get one with 72pin slots, I have 2x16MB in mine, I have also seen boards with 16 30pin-slots but 72pin RAM is a lot easier to come by than 4MB 30pin simms

also please use a different site for linking mobo specs, sta$on is terrible, full of ads... here's a good alternative: http://www.win3x.org/uh19/

Last edited by imi on 2021-10-13, 14:15. Edited 1 time in total.

Reply 17 of 27, by snufkin

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Picture of a KMC-A419-8 here: http://www.amoretro.de/wp-content/uploads/kmc … d_ali_m1419.jpg
Looks very similar to the layout of a KMC-40A here [edit, change link to UH19]: http://www.win3x.org/uh19/motherboards/159
or https://stason.org/TULARC/pc/motherboards/A/A … 6DLC-386DX.html

And that looks like it might support 32MB (8 4MB SIMMs).

[edit to add] I wonder if those 16MB SIMMs can be converted to working 4MB SIMMs by pulling A11 (pin 24) either high or low, through a 1k (ish) resistor? There's a convenient GND on pin 22, or +5V on pin 30. If the motherboard isn't driving A11 then maybe the reason they crash the board is because that address line is floating, so sometimes the wrong address is selected.

Reply 19 of 27, by cyberluke

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snufkin wrote on 2021-10-13, 14:15:
Picture of a KMC-A419-8 here: http://www.amoretro.de/wp-content/uploads/kmc … d_ali_m1419.jpg Looks very similar to the layout o […]
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Picture of a KMC-A419-8 here: http://www.amoretro.de/wp-content/uploads/kmc … d_ali_m1419.jpg
Looks very similar to the layout of a KMC-40A here [edit, change link to UH19]: http://www.win3x.org/uh19/motherboards/159
or https://stason.org/TULARC/pc/motherboards/A/A … 6DLC-386DX.html

And that looks like it might support 32MB (8 4MB SIMMs).

[edit to add] I wonder if those 16MB SIMMs can be converted to working 4MB SIMMs by pulling A11 (pin 24) either high or low, through a 1k (ish) resistor? There's a convenient GND on pin 22, or +5V on pin 30. If the motherboard isn't driving A11 then maybe the reason they crash the board is because that address line is floating, so sometimes the wrong address is selected.

Perfect thank you!