These days it's mostly converged on USB, but in the old days computers tended to have lots of different kinds of ports. In particular, I'm interested in:
- 9-pin serial
- 25-pin serial
- parallel printer
- external disk drive
- Atari joystick
- IBM keyboard
How much did each of these kind of ports cost to add to a 1980's home computer, in the old days? If exact figures aren't available, I'd be interested in an overall order of magnitude figure plus some idea of the differences, e.g. how much cheaper is 9-pin serial compared to 25-pin?
I'm specifically interested in Z80-based computers (e.g. ZX Spectrum).
Okay, for more specificity: yeah, ZX Spectrum is a representative particular machine, and I'm interested in total extra cost, the connector plus any chips needed to drive the port that weren't already necessary in the machine. I'm only interested in variable cost, not fixed, so the cost of developing any driver software can be ignored (though if it would be large, the cost of ROM space can't).