 The expansion port on the back of the computer is compatible with the ZX81, although some peripherals may not work due to conflicts with the 2K of extra ROM.The rear of the computer featured a TV output (without video backporch), EAR and MIC sockets for connecting to an external tape recorder, a JOYSTICK port using a DIN socket (that simulated the 5,6,7,8 and 0 keys), a ZX81 Compatible expansion port, space for a sound output socket, and a socket for the 9V external power supply.Since the joystick used the cursor keys, and due to the circuitry for the keyboard, it wasn't possible to detect diagonal directions correctly.