Looks like this one https://theretroweb.com/motherboards/s/m-tech … 8-pci-486-rev-1

The board looks like a decent PCI-based 486 mainboard. It's a good base for a 486 system, unless you specifically want a VLB system. The ATX-AT power adapters are no problem, except if you use a newer ATX supply and require -5V. Most people do not require -5V, but if you want to run the original Sound Blaster (not SB 16), you do. Both the 5x86-133 (at 3.3V) and the DX2-80 (at 5V) need a heatsink at least (peferably with some airflow) for stable operation. It's fine if you removed the heatsink just for the photo, but if you want to run the 5x86 without heatsink for an extended amount of time, I recommend you do not exceed 100MHz (e.g. by jumpering it as "AMD enhanced 486DX4" instead of "AMD 5x86").

Thanks for the info. The board is one that I had lying around so it doesn't have a heatsink. I am planning to get one for it though.

mkarcher wrote on 2022-11-21, 14:42:

jumpering it as "AMD enhanced 486DX4" instead of "AMD 5x86"

Is it safe to set the jumpers for a different cpu? I don't want to risk damaging it.
Could that be used to slow the cpu down or are there better ways? Especially since old dos games will run to fast on more powerful cpus.

Also I'm planning to build a custom case for this, does anyone have dimensions for the mount locations. Most pictures I've found are either for atx or don't list measurements.

Matrolisk wrote on 2022-11-23, 01:41:

mkarcher wrote on 2022-11-21, 14:42:

jumpering it as "AMD enhanced 486DX4" instead of "AMD 5x86"

Is it safe to set the jumpers for a different cpu? I don't want to risk damaging it.

It is extremely unlikely to cause permanent damage to either the board or the CPU if the CPU jumpering is wrong, with one exception: Do not feed 5V into 3.3V CPU. The specific mis-jumpering I suggested is known to be safe. There should be just one jumper different netween these two types, and that's the multiplier jumper (x4 for 5x86, x3 for AMD Enhanced DX4).

Matrolisk wrote on 2022-11-23, 01:41:

Could that be used to slow the cpu down or are there better ways? Especially since old dos games will run to fast on more powerful cpus.

In addition to slowing down the CPU from 133MHz to 100MHz by changing the internal multiplier, you can also slow down the CPU by lowering the bus clock from 33MHz to 25MHz. Way more effective is disabling L2 or both L1 and L2 cache in the BIOS setup, though.

Matrolisk wrote on 2022-11-23, 01:41:

Thanks for the info. The board is one that I had lying around so it doesn't have a heatsink. I am planning to get one for it though.

mkarcher wrote on 2022-11-21, 14:42:

jumpering it as "AMD enhanced 486DX4" instead of "AMD 5x86"

Is it safe to set the jumpers for a different cpu? I don't want to risk damaging it.

Am5x86 X4 and Intel DX2 use the same jumper settings.
Am5x86 X3 and DX4 use the same jumper settings

So yes, if your board doesn't show settings for Am5x86 X3, just use the setting it shows for DX4

debs3759 wrote on 2022-11-23, 08:33:

Am5x86 X4 and Intel DX2 use the same jumper settings.
Am5x86 X3 and DX4 use the same jumper settings

It's not that easy, but the idea is correct. The board in question supports L1 write-back cache and System Management Mode. Standard Intel DX2 processors use 5V instead of 3.3V. If we explicitly say "the voltage jumpers are not considered", and furthermore only talk about the write-back enhanced versions of the Intel DX2 and Intel DX4, this statement is correct to the best of my knowledge, though. As the write-back enhanced DX2 processors were available only when a DX4 was already considered an entry-level processor, they didn't make it into all motherboard manuals. These late DX2 variants found more use in specialized embedded hardware. The classic DX/DX2 jumpering (no SMM, no L1WB) is considerably different from jumpering for the new-fangled processors.

If you were using an auto-voltage board that doesn't try to make use of the "warm reset" that skips L1 flush, SMM and only supports L1 in write-through mode, but it still has the DX4 clock multiplier selection jumper, you can indeed use the same jumpering for an 5x86 in x4 mode and a classic DX2.

It is that easy on a board where you can set WB/WT. The settings on the boards I checked are identical.