Good old laplink. I've still got a "hydra" cable in my desk drawer. Back in the 90s I used the parallel port to interface a PC to a TRS-80 to allow me to store

Good old laplink. I've still got a "hydra" cable in my desk drawer. Back in the 90s I used the parallel port to interface a PC to a TRS-80 to allow me to store games on the PC. As another commenter has mentioned, the parallel cable isn't fully bidirectional so I used the printer ready, paper out and other signals as imput lines and wrote a nybble (half a byte) based protocol between the two. Fun times.