A drum machine consists of drum hits that have been sampled/recorded into a playback device as well as filters, levels, effects (sometimes) and other things to manipulate the sample. The drum hits are arranged and triggered using either an onboard hardware sequencer or with MIDI using a software sequencer. It is used in all forms of music. The most famous drum machines ever are the x0x series by Roland. The Roland TR-808 and Roland TR-909 kick drums are used in 99% of all House and Techno songs.