[1] In a sense it is not a true module version of a JD-800 as it has many expanded features and as a result the two are incompatible in exchanging presets.

It is equipped with 6 MB of ROM containing sampled PCM waveforms, four sets of stereo outputs that are assignable to individual, internal, instruments, and standard MIDI in/out/through ports.

JD-990 has a large LCD display[2] and programming takes place through a keypad on the front panel of the unit.

The JD-990 has been used by artists such as Klaus Schulze,[5] Paul Shaffer,[6][7][8] Steve Duda,[9] Vangelis, The Prodigy, Apollo 440, ATB, and Mirwais.

[3] Apollo 440 used the JD-990 for atmospheric sounds on the track "The Machine in the Ghost", on the album Gettin' High on Your Own Supply.