Certain early arcade machines made use of sound cards to achieve playback of complex audio waveforms and digital music, despite being already equipped with onboard audio. An example of a sound card used in arcade machines is the Digital Compression System card, used in games from Midway. For example, Mortal Kombat II on the Midway T Unit hardware. The T-Unit hardware already has an onboard YM2151 OPL chip coupled with an OKI 6295 DAC, but said game uses an added on DCS card instead. The card is also used in the arcade version of Midway and Aerosmith's Revolution X for complex looping BGM and speech playback (Revolution X used fully sampled songs from the band's album that transparently looped- an impressive feature at the time the game was released).