Initially sold for ¥49,000
The Yamaha MK1 was a music keyboard part of the YIS ecosystem, supposedly just a controller. An additional FM synthesizer board had to be purchased (the PU1-BM) and installed in the central unit PU1. Details about such synthesizer are unknown. The keyboard is attached to the main computer with a ribbon cable,
The concept and shape is suspiciously similar to the YK10 music keyboard that was later sold by Yamaha to be used with SFG01 or SFG05 FM sound modules for MSX computer, although this one is shaped in a similar fashion to the KB1 and has wooden sides.