Kempston Interface
The Kempston Interface, produced by Kempston Micro Electronics, was the generic name for any interface on Sinclair's ZX Spectrum series of computers that allowed joysticks complying with the de facto Atari 2600 standard to be used with the machine. It was one of the most widely supported standards on the machine. The interface itself would be attached to the computer's rear expansion port with a single joystick port on the front or top of the system.
It came out as the clear winner against other standards such as Protek's cursor-based solution and the Fuller standard during the days of the 48K Spectrum. However, when Amstrad released the ZX Spectrum +2, the computer featured a built-in joystick interface that was software-compatible with Sinclair's ZX Interface 2 standard. Unfortunately, the bundled SJS-1 joystick was electrically incompatible with the Atari standard. The Interface 2 standard simulated keypresses on the numerical keys (1 to 5 and 6 to 0 being left, right, down, up, fire for the 'left' and 'right' joysticks respectively) and hence were ideal for games with no official joystick support but in which the keys could be redefined.
Problems had also been reported with the Kempston Interface breaking down on the newer models and it faded slowly into obscurity, although the option to use Kempston joysticks remained in games until the end of the computer's shelf life.