They're basically completely different other than broad architectural strokes. Different CPU ISA, the keys are sampled through a matrix rather than a bit bange

They're basically completely different other than broad architectural strokes. Different CPU ISA, the keys are sampled through a matrix rather than a bit banged shift register setup, audio channels are pretty different, GPU is internally pretty different (LCD allows pauses in the pixel stream unlike a CRT so the GPU uses that), etc.