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.

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.

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.

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

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.

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.

386 boards with support for 16 MB 30-pin SIMMs are uncommon.

I've got a 386 with 64 MB of RAM, but it's 2 x 32 MB 72-pin SIMM.

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.

You can get 4MB(9) x 8 giving you 32MB

I bought this: https://www.ebay.com/itm/124443425902

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

Board is KMC-A419-8 VER 1.0, no jumpers for memory.

Ok, I see there are only 4mb modules and 16mb modules. No 8mb modules. I guess these 16mb modules are good only for sound blaster 😀

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.

I thought you might have had this board

https://stason.org/TULARC/pc/motherboards/I/I … -386-M-321.html

* that was the other poster 😁

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/

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.

cyberluke wrote on 2021-10-13, 14:05:

I think PC Chips were quite good.

🤣

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 […]
Show full quote

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!