The YS100 is basically a TX81Z keyboard with added effects. It's up to 8-part multi-timbral with 100 presets and 100 user settings. It's a typical 4-op Yamaha, can use TX81Z, DX100 patches but with added on-board effects (reverb, delay echo and distatortion, inc gate and reverse gate reverbs). On the whole not bad. Also look out for YS200 - as above but with added 8 track sequencer!