The Roland TR-909 Rhythm Composer is a partially analog, partially sample-based, drum machine introduced by the Japanese Roland Corporation in 1983. The brainchild of Tadao Kikumoto, the engineer behind the Roland TB-303, it features a 16-step step sequencer and a drum kit that aimed for realism and cost-effectiveness. It is fully programmable, and like its predecessor, the TR-808, it can store entire songs with multiple sections, as opposed to simply storing patterns. It was the first MIDI-equipped drum machine. Around 10,000 units were produced.^{[citation needed]}

As with the TB-303, the realism of the TR-909 was severely limited by technical constraints, and this showed when the machines were released at relatively low prices before its rise in popularity, coinciding with the beginnings of techno and acid. More expensive, sample-based drum computers were better at faithfully reproducing real drum sounds, while the TR-909 sounded synthetic.

The drum kit contains the following sounds:

All drums except for the hi-hats and cymbals are synthetically generated; there is an oscillator circuit with a dedicated filter and envelope curve. The hi-hats and cymbals are 6-bit samples, compressed and combined with a volume envelope curve (and tuning) to allow slight modification. Thanks to the analog circuitry, various aspects of the drum sound can be modified (pitch, attack, decay).

Jeff Mills (born 18 June 1963 in Detroit, Michigan) is an American techno DJ and producer.

Starting in the early 1980s, Mills, using the name "The Wizard", was a recurring guest DJ on "The Electrifying Mojo" radio show on WJLB. He performed DJ tricks like beat juggling and scratching during his sets, some of which were pre-recorded.

Mills and former Parliament bass player 'Mad' Mike Banks were founding members of Detroit techno collective Underground Resistance (UR), which embraced revolutionary rhetoric and only appeared in public dressed in ski masks and black combat suits.

Mills never officially left UR, but did relocate from Detroit, first to New York, then Berlin (as a resident at the Tresor club), and then Chicago. There in 1992, with fellow Detroit native Robert Hood, he set up the record label Axis, and later, sub-labels Purpose Maker, Tomorrow, and 6277, all aiming for a more minimal sound than most of the techno being produced in those years.

In his DJ sets, Mills usually uses three decks, a Roland TR-909 drum-machine, and up to seventy records in one hour. Mills' Exhibitionist DVD, from 2004, features him mixing live on three decks and CD player in a studio.