It depends on what you mean by "computer". A lot of the older calculators still work. I think many portable TRS-80's still work? VIC-20, C64... the display is

It depends on what you mean by "computer". A lot of the older calculators still work. I think many portable TRS-80's still work? VIC-20, C64... the display is the weakest point. The above devices use VFDs or 7-segment LCDs. RS-232-level 7&8-bit ASCII serial communications are probably the lingua franca of computers and will continue to be, so if your devices can send text across the serial port you should be able to find devices far into the future to communicate with your old computer.