This is an external ROM card and expansion bus breakout board for the Sinclair ZX Spectrum. It will work with the Harlequin or standard Spectrum. There's a jumper to select which ROM image is active (Spectrum internal ROM or ROM on the card) and a reset button (Press and hold reset and change the jumper over, then release reset). Interface 2 cartridge ROMs can be burned onto EPROM and run from this card. Use 27c128 EPROMs. The board is designed to take a Textool ZIF socket or similar Chinese copy. Not many components here, so it's a quick build. Component values are shown on the PCB.