And it's a curious feeling to stumble upon memories I haven't touched in years -- I used to love idly disassembling computer mice, cleaning out fuzz and gunk from the little rollers and the ball, and putting them back together. It was one of things I had to consciously stop myself from doing if I was sitting at someone else's desk.
Optical mice have been around so long now, I had completely forgotten how they used to work, and that odd little pleasure of maintaining a simple mechanical device.
Edit: this confuses me, though: The basic approach — pairing a freely-rolling ball with a optoelectronic system — was used by generations of mice that followed, changing only incrementally until optical mice did away with trackballs altogether.
Is that right? The mice I was always taking apart normally detected the motion of the trackball with two little white rollers, for Y and X motion. That's neither of these systems.