SD Microsystems was a serious software house based in the UK, established in 1985 and run by Steve Denson. It remained a supporter of the CPC long after most comparable businesses had ended their CPC lines. Indeed, it still lists some CPC products for sale in the 'clearance' section of its website, although all other sales have stopped. It also continues to supply consumables such as 3in discs and DMP-2000 printer ribbons.
The company took over LocoScript Software in 1999, thereby laying claim to be the inheritor of the Locomotive Software tradition. It consequently owns the copyright to Locomotive BASIC, AMSDOS and the CPC firmware.