Vintage Synth Explorer describe it as,
One of the most popular digital synths ever was the DX7 from Yamaha, released in 1983. It featured a whole new type of synthesis called FM (Frequency Modulation). It certainly is not analog and it is difficult to program but can result in some excellent sounds! It is difficult because it is non-analog and thus, a whole new set of parameters are available for tweaking, many of which seemed counter-intuitive and unfamiliar. And programming had to be accomplished via membrane buttons, one data slider and a small LCD screen.