Microsoft Bus/InPort was the fastest PC mouse interface until PS2, and easiest to emulate. Checking mouse position cost one interrupt + 10 in/out port opcodes. PS2 is one interrupt + 4 in port opcodes + out interrupt acknowledge, but there is tons of commands one has to implement. Serial mouse is simple but costs 3 interrupts and uses slow data transfer speed (default 1200bps).
Microsoft didnt totally abandon its older InPort mice, they actually sold InPort to Serial/PS2 adapter (C3K9ILMA) allowing one to reuse old inport mouse in newer computer https://www.ebay.com/itm/375576855239
Good info on Alps 64H101. Long time ago when looking at inPort card I couldnt figure out how it worked with only one cd4020 counter. I guessed incorrectly 64H101 to be some 74H101 version. Now its obvious cd4020 is used for generating interrupts.
rasz•1mo ago
Microsoft didnt totally abandon its older InPort mice, they actually sold InPort to Serial/PS2 adapter (C3K9ILMA) allowing one to reuse old inport mouse in newer computer https://www.ebay.com/itm/375576855239
Good info on Alps 64H101. Long time ago when looking at inPort card I couldnt figure out how it worked with only one cd4020 counter. I guessed incorrectly 64H101 to be some 74H101 version. Now its obvious cd4020 is used for generating interrupts.