How Things Work

and Stuff. (At CMU, CFA - which some people said stood for "Can't Friggin Add", while others said it stood for "Can't Friggin Spell" :P - had three courses, the first "How People Work", and the second "How Things Work", and the third "How People Work and Things").

I've been studying computers for a long time. I got started seriously the summer I visited colleges (between Sophomore and Junior year in High School). I got a book on DOS programming from the MIT bookstore, and read it the whole rest of the trip.

It's only today that I figured out why the "mouse" and "keyboard" PS/2 connectors on the back of the computer are different!

You know which ones I mean. The are different colors, with the plugs on the mouse and keyboard color coded to match.

I always looked at them, and said "Why should it matter?" The plugs are the same, why can't the computer just figure it out!

Then I saw the figure at the OSDev Wiki page for the keyboard.

The IRQ line from the keyboard connector is hardcoded to IRQ 1, and the mouse goes to IRQ 12. There is no identifier from the hardware to easily figure out which is which (they both send bytestreams of input, worse they send the data to the same port). You might be able to decode which is more likely, but it isn't easy. Then you would have to switch your interrupt handlers. I guess most people don't bother.