The One Demon wrote on 2025-11-12, 08:28:

I've tried looking these up, but I'm having trouble 🤣. Does anyone know how big these SIMM RAM sticks are? I found the top RAM sticks 2 larger chips and 1 smaller chip on them. They're either 2MB each per large chip, or total I'm not entirely sure?

Interesting that the second lot of RAM is tinned, rather than gold.

These are from the same PC as the battery corroded Asus motherboard.

The trick with RAM is to find the datasheet of the chips on the modules, or just a sufficiently clear product name.

The SIMMs with 9 identical chips have OKI M511000A-70J chips. Googling that gets you:

1,048,576-Word x 1-Bit DYNAMIC RAM : FAST PAGE MODE TYPE

1048576 is 1M x 1 so 1Mbit total. Eight of those gives you and 8-bit wide interface (which is correct for 30p SIMMs and an indication you're looking at the right info) an 8 x 1Mb = 8Mb = 1MB. The ninth gives you parity.

So this is a 1MB FP DRAM module with parity rated to run at 70ns. And yes, the SIMM has tinned pads. Back in the day manuals went out of their way to tell you that if your motherboard has tinned pins on the SIMM slots you should only use tinned SIMMs and if your slots have gold pins you should only use SIMMs with gold pads. I can see from electrochemical theory how mismatched metals could lead to corrosion, but in practice people mixed and matched and I can't say I've ever seen a case where - even after decades - a mismatch led to bad connections. I have however seen tinned SIMMs having poor connectivity due to oxidation regardless of the SIMM slot pins.

The 3-chip module has two big chips and one small one. Knowing that the SIMM must be 8 bits wide (plus a ninth for parity) that tells us the 2 chips need to be x 4 wide, and the third x 1 (and 1/4 of the capacity of the big ones). Sure enough:
km44c4100aj-6

4M x 4Bit CMOS Dynamic RAM with Fast Page Mode

So, 4 x 4 = 16Mb = 2MB and 4 bits wide.

The BP41C4000-6 doesn't seem to get any hits for relevant datasheets, but is mentioned in a couple of sites selling 4MB parity SIMMs. So it's certain to be a 4M x 1 fast page DRAM chip.

That makes these SIMMs 4MB FP DRAM with parity, rated to run at 60ns.

In general 70ns is good for up to ~60MHz, with 60ns needed for 66MHz and/or for really tight timings. And 386 had pretty tight timings, being able to get memory access down to 2 cycles. 1 cycle at 40MHz would be 25ns, so with 2 cycles you could hit 50ns. That's too fast for either of these SIMMs (at least: they're not rated for that. They might run faster than specced though...). Conversely with an extra wait state you go up to 75ns, in which case either is good enough. So based on spec these sets of SIMMs should both allow the same timings on this board/with this CPU. However if you want to push things, I'd sooner bet on the 60ns part than the 70ns. With 33MHz things would be different as then a cycle is 30ns and so you could use 60ns memory to allow access in 2 cycles where you couldn't (at least on paper) with 70ns, needing that third cycle.

The One Demon wrote on 2025-11-12, 08:30:

PC@LIVE wrote on 2025-11-12, 02:39:

The One Demon wrote on 2025-11-12, 00:50:

I had a look on eBay and that card might actually cover the entire cost or almost haha. I'll give it a whirl just to see it in action and experience it, but yeah.

Someone's offered this motherboard https://theretroweb.com/motherboards/s/ecs-us3486, well it's actually FX-3000D on the board, I can see some differences in the boars vs the one linked, but that's the closest mobo I could see on there. Unsure on price yet.

In that motherboard of your link, you can install both 386DX and 486 CPUs, of course or one or the other, I have one with a 486DLC, which would be a middle ground between 386 and 486, so if it works and doesn't cost too much, it would be a good replacement for those who have a broken 386.

Thanks! If I'm looking at it right, it has the 386DX-40 integrated/soldered on, and then another slot if you wanted a FPU or 486 instead right?

Yes, the welded 386DX still seems removable, so to replace the CPU in case of upgrade, if you have a 486 DX, you can put it in the socket where the 387 (Coprocessor) also goes, but if you keep the 386 you can add the 387, if instead you put a 486 you have to remove the 386, and I'm pretty sure, that you should change some jumpers, to make it work.
However, the maximum could be a 486DX2, because the board has a voltage reducer, so only 5V CPU.

dionb wrote on 2025-11-12, 09:12:

The trick with RAM is to find the datasheet of the chips on the modules, or just a sufficiently clear product name. […]
Show full quote

The One Demon wrote on 2025-11-12, 08:28:

I've tried looking these up, but I'm having trouble 🤣. Does anyone know how big these SIMM RAM sticks are? I found the top RAM sticks 2 larger chips and 1 smaller chip on them. They're either 2MB each per large chip, or total I'm not entirely sure?

Interesting that the second lot of RAM is tinned, rather than gold.

These are from the same PC as the battery corroded Asus motherboard.

The trick with RAM is to find the datasheet of the chips on the modules, or just a sufficiently clear product name.

The SIMMs with 9 identical chips have OKI M511000A-70J chips. Googling that gets you:

1,048,576-Word x 1-Bit DYNAMIC RAM : FAST PAGE MODE TYPE

1048576 is 1M x 1 so 1Mbit total. Eight of those gives you and 8-bit wide interface (which is correct for 30p SIMMs and an indication you're looking at the right info) an 8 x 1Mb = 8Mb = 1MB. The ninth gives you parity.

So this is a 1MB FP DRAM module with parity rated to run at 70ns. And yes, the SIMM has tinned pads. Back in the day manuals went out of their way to tell you that if your motherboard has tinned pins on the SIMM slots you should only use tinned SIMMs and if your slots have gold pins you should only use SIMMs with gold pads. I can see from electrochemical theory how mismatched metals could lead to corrosion, but in practice people mixed and matched and I can't say I've ever seen a case where - even after decades - a mismatch led to bad connections. I have however seen tinned SIMMs having poor connectivity due to oxidation regardless of the SIMM slot pins.

The 3-chip module has two big chips and one small one. Knowing that the SIMM must be 8 bits wide (plus a ninth for parity) that tells us the 2 chips need to be x 4 wide, and the third x 1 (and 1/4 of the capacity of the big ones). Sure enough:
km44c4100aj-6

4M x 4Bit CMOS Dynamic RAM with Fast Page Mode

So, 4 x 4 = 16Mb = 2MB and 4 bits wide.

The BP41C4000-6 doesn't seem to get any hits for relevant datasheets, but is mentioned in a couple of sites selling 4MB parity SIMMs. So it's certain to be a 4M x 1 fast page DRAM chip.

That makes these SIMMs 4MB FP DRAM with parity, rated to run at 60ns.

In general 70ns is good for up to ~60MHz, with 60ns needed for 66MHz and/or for really tight timings. And 386 had pretty tight timings, being able to get memory access down to 2 cycles. 1 cycle at 40MHz would be 25ns, so with 2 cycles you could hit 50ns. That's too fast for either of these SIMMs (at least: they're not rated for that. They might run faster than specced though...). Conversely with an extra wait state you go up to 75ns, in which case either is good enough. So based on spec these sets of SIMMs should both allow the same timings on this board/with this CPU. However if you want to push things, I'd sooner bet on the 60ns part than the 70ns. With 33MHz things would be different as then a cycle is 30ns and so you could use 60ns memory to allow access in 2 cycles where you couldn't (at least on paper) with 70ns, needing that third cycle.

Thanks for the awesome write up mate! Makes it much easier to work out, good to know I was somewhat on the right track haha.

So I'd be better off just using the four 4MB sticks then, doubly so if I want to try to overclock the ram timings to try and get 50ns? As far as I can find, 16MB is more than enough for a 386 DOS system anyways.

PC@LIVE wrote on 2025-11-12, 09:26:

The One Demon wrote on 2025-11-12, 08:30:

PC@LIVE wrote on 2025-11-12, 02:39:

In that motherboard of your link, you can install both 386DX and 486 CPUs, of course or one or the other, I have one with a 486DLC, which would be a middle ground between 386 and 486, so if it works and doesn't cost too much, it would be a good replacement for those who have a broken 386.

Thanks! If I'm looking at it right, it has the 386DX-40 integrated/soldered on, and then another slot if you wanted a FPU or 486 instead right?

Yes, the welded 386DX still seems removable, so to replace the CPU in case of upgrade, if you have a 486 DX, you can put it in the socket where the 387 (Coprocessor) also goes, but if you keep the 386 you can add the 387, if instead you put a 486 you have to remove the 386, and I'm pretty sure, that you should change some jumpers, to make it work.
However, the maximum could be a 486DX2, because the board has a voltage reducer, so only 5V CPU.

Alright no worries, thanks! I think I'll just keep the soldered 386 in this one probably, I ended up also buying the other PC linked by dionb with the included monitor and keyboard. (486 I think it is)

The One Demon wrote on 2025-11-12, 09:43:

PC@LIVE wrote on 2025-11-12, 09:26:

The One Demon wrote on 2025-11-12, 08:30:

Thanks! If I'm looking at it right, it has the 386DX-40 integrated/soldered on, and then another slot if you wanted a FPU or 486 instead right?

Yes, the welded 386DX still seems removable, so to replace the CPU in case of upgrade, if you have a 486 DX, you can put it in the socket where the 387 (Coprocessor) also goes, but if you keep the 386 you can add the 387, if instead you put a 486 you have to remove the 386, and I'm pretty sure, that you should change some jumpers, to make it work.
However, the maximum could be a 486DX2, because the board has a voltage reducer, so only 5V CPU.

Alright no worries, thanks! I think I'll just keep the soldered 386 in this one probably, I ended up also buying the other PC linked by dionb with the included monitor and keyboard. (486 I think it is)

Just curious, which of the photos is the board being offered? Just asking cause in the first photo it's soldered onto the board, but in the other photos it's on one of those little adapter boards.

The One Demon wrote on 2025-11-12, 09:35:

[...]
Thanks for the awesome write up mate! Makes it much easier to work out, good to know I was somewhat on the right track haha.

So I'd be better off just using the four 4MB sticks then, doubly so if I want to try to overclock the ram timings to try and get 50ns? As far as I can find, 16MB is more than enough for a 386 DOS system anyways.

20MB of RAM is an impressive amount for a 386, and vastly more than any game-oriented stuff that would run on a PC like that could sensibly use. Tbh for 386 games 4MB would be more than enough. I suspect the previous owner was running Windows 3.1 on it. Windows itself will run fine on 4MB, but application software eats up RAM quickly. I ran Win 3.1 on my P60 and my 8MB really wasn't enough with Word 6.0 and Excel running at the same time. With 72p SIMMs I could upgrade to 16MB, but with 30p SIMMs and 4x 1MB already installed you have to choose between adding another 4MB, which would not have been enough, or adding 16MB, which would have been viciously expensive but would have stopped the system thrashing with big documents loaded once and for all. It appears they chose the latter.

So yes, just stick with the 4x 4MB unless you start doing something exotic. In fact, If you were to come across a 486 system with 30p SIMM slots needing RAM, I'd say put 4x 4MB in there and just stick with 4x 1MB in the 386.

sunkindly wrote on 2025-11-12, 10:18:

The One Demon wrote on 2025-11-12, 09:43:

PC@LIVE wrote on 2025-11-12, 09:26:

Yes, the welded 386DX still seems removable, so to replace the CPU in case of upgrade, if you have a 486 DX, you can put it in the socket where the 387 (Coprocessor) also goes, but if you keep the 386 you can add the 387, if instead you put a 486 you have to remove the 386, and I'm pretty sure, that you should change some jumpers, to make it work.
However, the maximum could be a 486DX2, because the board has a voltage reducer, so only 5V CPU.

Alright no worries, thanks! I think I'll just keep the soldered 386 in this one probably, I ended up also buying the other PC linked by dionb with the included monitor and keyboard. (486 I think it is)

Just curious, which of the photos is the board being offered? Just asking cause in the first photo it's soldered onto the board, but in the other photos it's on one of those little adapter boards.

Well fuck, I didn't notice that... I probably just got scammed then..

The One Demon wrote on 2025-11-13, 00:39:

sunkindly wrote on 2025-11-12, 10:18:

The One Demon wrote on 2025-11-12, 09:43:

Alright no worries, thanks! I think I'll just keep the soldered 386 in this one probably, I ended up also buying the other PC linked by dionb with the included monitor and keyboard. (486 I think it is)

Just curious, which of the photos is the board being offered? Just asking cause in the first photo it's soldered onto the board, but in the other photos it's on one of those little adapter boards.

Well fuck, I didn't notice that... I probably just got scammed then..

Optimistically, if you were intending to keep it as a 386 I don't think it's that big of a deal unless you get something completely different than what was advertised. Especially since you have a 486 on the way.

sunkindly wrote on 2025-11-13, 00:45:

The One Demon wrote on 2025-11-13, 00:39:

sunkindly wrote on 2025-11-12, 10:18:

Just curious, which of the photos is the board being offered? Just asking cause in the first photo it's soldered onto the board, but in the other photos it's on one of those little adapter boards.

Well fuck, I didn't notice that... I probably just got scammed then..

Optimistically, if you were intending to keep it as a 386 I don't think it's that big of a deal unless you get something completely different than what was advertised. Especially since you have a 486 on the way.

Well he didn't say he had multiple, only sent the one photo of the soldered 386 that I posted, the rest were definitely of the same board in the other photos and can't find a match with reverse google image search.. So there's at least some hope! Just sus now because I didn't realise that before 😅 (as in not sure if one will even be sent)

dionb wrote on 2025-11-12, 11:53:

The One Demon wrote on 2025-11-12, 09:35:

[...]
Thanks for the awesome write up mate! Makes it much easier to work out, good to know I was somewhat on the right track haha.

So I'd be better off just using the four 4MB sticks then, doubly so if I want to try to overclock the ram timings to try and get 50ns? As far as I can find, 16MB is more than enough for a 386 DOS system anyways.

20MB of RAM is an impressive amount for a 386, and vastly more than any game-oriented stuff that would run on a PC like that could sensibly use. Tbh for 386 games 4MB would be more than enough. I suspect the previous owner was running Windows 3.1 on it. Windows itself will run fine on 4MB, but application software eats up RAM quickly. I ran Win 3.1 on my P60 and my 8MB really wasn't enough with Word 6.0 and Excel running at the same time. With 72p SIMMs I could upgrade to 16MB, but with 30p SIMMs and 4x 1MB already installed you have to choose between adding another 4MB, which would not have been enough, or adding 16MB, which would have been viciously expensive but would have stopped the system thrashing with big documents loaded once and for all. It appears they chose the latter.

So yes, just stick with the 4x 4MB unless you start doing something exotic. In fact, If you were to come across a 486 system with 30p SIMM slots needing RAM, I'd say put 4x 4MB in there and just stick with 4x 1MB in the 386.

Awesome, thanks for that. I'll keep that in mind! 😀