It's called a KVM.

They come in many styles. Serial might not be as easy as usb or ps2 though.

https://www.aten.com/global/en/products/kvm/c … switches/cs62s/

That is one example of many.

I would have to look for a switch with DB-15 VGA connectors, DIN-5 for the keyboard and DB-9 for the mouse. My keyboard has an old DIN 5 connection. Can it work with a MIDI extension cable? And with the mouse, what should the cable be like?
Regards.

https://www.amazon.com/CableWholesale-Keyboar … 6/dp/B00SNCM1R2

https://www.amazon.com/CablesOnline-MiniDin6- … 2/dp/B00HGI5JPA

No idea about midi

Hi,
I have purchased DIN-5 MIDI cables and have tried to connect them to the computers. I noticed that when connecting, it was forced. Then I realized that the pins on the MIDI cable are slightly thicker than the DIN-5 pins on the AT keyboard. Have I forced the connectors on the motherboard? Where can I get DIN-5 Male-Male AT keyboard cables? Thank you very much.

In the photo, the one on the left is a MIDI connector, the one on the right is an AT connector

Is the DIN-5 MIDI cable used to connect AT keyboards?

It should be possible to use a newer KVM switch with multiple DIN5<->PS/2 converters. PS/2 extensions cables are often bundled with those switches.
I am not sure that every MIDI cable would work - MIDI electrical specification says that pins 1 and 3 are "not connected" but they are needed to have a functional keyboard connection - at least pin 1, as it carries the clock signal to the keyboard.

CAUTION: not there is no such thing a universal PS/2 to serial mouse adapter. Learned the hard way by blowing up a motherboard because I didn't use the correct adapter...

See thread here:
PS/2 - serial mouse adaptor

Something like this might be your only save bet: https://www.ebay.com/itm/335504101119

I think your best chance is searching ebay or wherever for a PS2 KVM.
Most will have a VGA and not DVI, etc connection but double check.

The good thing is these are still cheap and easy to find.
You would need the DIN5 to PS/2 adapter like the first link in myne's post, which are also cheap and easy to find.

Not many KVM's support serial mice and serial to PS/2 adapters rarely work.
You could get a second "RS232 Switch box" like the one below, personally though I'd just have 2 mice on my desk one for each PC.

https://www.jw.com.au/product/4-way-db9-rs232 … M0aAl4dEALw_wcB