There was a time when if you bought a USB mouse, in the box was also an adapter to allow it to be used with the older PS/2 interface. And if you were to go back a few more years into the past ...

For instance, a decent PS/2 to USB adapter will cost you as much as the Zero did, if not more. But if you just need to drive your Pi Zero from your old Model M (we hear you!) you’ve got to do it ...

The problem, according to Chen, is that "USB and PS/2 are completely different protocols that are not compatible in any way. The adapter was purely mechanical (passive). It connected one set of ...