Some of the later 486 computers (especially PCI ones) and Pentium computers are likely to have an internal PS/2 mouse port at least, so you just may need to find a bracket for it.

Just found that one port is a DB-25 Serial/Com port and the other a DE-9 Serial RS232...

Sounds like you have an AT port on one of them, but you already have a converter. You could also try a serial mouse with that machine. I'm a bit confused about what you mean by two serial ports of different sizes. It might be useful to take a picture for us.

The big keyboard port is an AT keyboard port. It's electrically compatible with a PS/2 keyboard port, and all you need is a passive physical adapter to connect a PS/2 keyboard.

If there is no PS/2 mouse port, these systems were originally used with a serial mouse. So it's up to you to grab one, figure out what kind of conversion device you want to use, or as Disruptor said, check the motherboards and see if there is an internal PS/2 mouse port header to which you could wire up a port.

There's no way the 486 takes a keyboard on a serial port if it's a normal desktop PC. It should have an AT keyboard port just like your Pentium.

You guys were right, seems I have an AT port in each of the computers for keyboard. I will buy a converter to PS2 and connect my PS2 keyboard there. Regarding mouse, are you aware if there's still any mouses around on sale using DB9? what sort of solutions are you using to connect your mouses to your DB9 ports?

I got some db9 to ps2 converters in the meantime, hope they work! 😀

You could look for an old serial mouse or a kvm switch that converts ps/2 to serial.

Achilles2 wrote on 2024-06-17, 18:55:

You guys were right, seems I have an AT port in each of the computers for keyboard. I will buy a converter to PS2 and connect my PS2 keyboard there. Regarding mouse, are you aware if there's still any mouses around on sale using DB9? what sort of solutions are you using to connect your mouses to your DB9 ports?

They aren't made any more, but there are plenty on ebay including new old stock if you're willing to pay for one.
They are all ball mice. The only optical serial mice were the ones with a special mouse pad.
The issue is the serial port doesn't provide enough power for an optical mouse.

A converter like this should work or the conversion of the serial mouse need an active converter?

AlessandroB wrote on 2024-06-17, 20:56:

A converter like this should work or the conversion of the serial mouse need an active converter?

If you have a 90s PS/2 mouse that also can speak RS-232 through its connector (sometimes they will say that underneath), like one that came with a passive adapter for serial, it's possible that kind of adapter will work. But the pinout was not standardized. And you can't just grab a 2000s optical mouse and hook it up to that. It won't work.

Achilles2 wrote on 2024-06-17, 19:14:

I got some db9 to ps2 converters in the meantime, hope they work! 😀

they wont, require special old mice and those werent standardized even in same brand (ms had two wiring convention)
you need one of those PS/2 mouse to Serial Port adapter or similar projects

AlessandroB wrote on 2024-06-17, 20:56:

A converter like this should work or the conversion of the serial mouse need an active converter?

They may work with mice that were designed for dual use RS-232 & PS/2 and should be considered as non-standardized custom adapters.
But basically that are ballpoint mice since RS-232 just allows a very low power consumption.

Achilles2 wrote on 2024-06-17, 19:14:

I got some db9 to ps2 converters in the meantime, hope they work! 😀

Are you talking about passive adapters (like pic above) or active converters (things with a chip on/in them)?

The latter should definately work with basically anything that talks PS/2 protocol but the former will only work with mice that talk RS232 serial. Worst-case, given the higher voltage levels on serial vs PS/2, you might even cause damage to a PS/2-only mouse on a passive converter to serial.

For questions like this it's always useful to specify what hardware you bought, or at least give a link or pic for the item.