The most basic equipment that is necessary for a standard disc jockey to perform consists of the following: 1. sound recordings in preferred medium (eg. vinyl records, compact discs, mp3) 2. at least two devices for playback of sound recordings, for the purpose of alternating back and forth to create continuous playback (eg. record players, compact disc players, mp3 players) 3. a sound system for amplification of the recordings (eg. portable audio system, radio wave broadcaster). The addition of a mixer (used to mix the sound of the two playback devices), a microphone (used to amplify the human voice), and headphones (used to listen to one recording while the other is playing, without outputting the sound to the audience) is strongly recommended, but not required. Other types of equipment can also be added, including samplers, drum machines, effects processors, slipmats, and computerized performance systems.
Karaoke is a form of entertainment in which an amateur singer or singers sing along with recorded music on microphone. A basic karaoke machine consists of audio input, a means of altering the pitch of the music (not the singer) and an audio output. Most common machines are audio mixers with microphone input built-in with CD+G, Video CD, Laser Disc, or DVD players. CD+G players use a special track called subcode to encode the lyrics and pictures displayed on the screen, while the other formats natively display both audio and video. Many low-end entertainment systems (boom boxes etc) have a karaoke mode that attempts to remove the vocal track from general (non-karaoke) audio CDs. This is done by center removal which exploits the fact that in most music the vocals are in the center.
References: Wikipedia article "Disc jockey", Wikipedia article "Karaoke"
