Originally, broadcasting  authorities required a licensed operator to run every station at all times, meaning that every DJ had to pass an exam to obtain a license to be on-air, if their duties also required them to ensure proper operation of the transmitter. This was often the case on overnight and weekend shifts when there was no broadcast engineer present, and all of the time for small stations with only a contract engineer on call.

Early automation systems were electromechanical systems which used relays. Later systems were "computerized" only to the point of maintaining a schedule, and were limited to radio rather than TV. Music would be stored on reel-to-reel audio tape. Sub-audible tones on the tape marked the end of each song. The computer would simply rotate among the tape players until the computer's internal clock matched that of a scheduled event. When a scheduled event would be encountered, the computer would finish the currently-playing song and then execute the scheduled block of events. These events were usually advertisements, but could also include the station's top-of-hour station identification, news, or a bumper promoting the station or its other shows. At the end of the block, the rotation among tapes resumed.

Advertisements, jingles, and the top-of-hour station identification required by law were often on "carts". Short for cartridges, these were endless tapes similar to 8-track tapes, and looked nearly identical as well. Mechanical carousels would rotate the carts in and out of multiple tape players as dictated by the computer. Time announcements were provided by a pair of dedicated cart players, with the even minutes stored on one and the odd minutes on the other. This meant an announcement would always be ready to play, even if the minute was changing when the announcement was triggered. The system did require attention throughout the day to change reels as they ran out and reload carts. It became obsolete when a method was developed to automatically rewind and re-cue the reel tapes when they ran out, extending 'walk-away' time indefinitely.

Modern systems typically run on computer hard disk, where all of the music, jingles, advertisements, voice tracks, and other announcements are stored. The audio files would be either compressed or uncompressed, or often with only minimal compression as a compromise between file size and quality. For radio, these disks were usually in computers, sometimes running their own custom operating systems, but more often running as an application like Windows NT or later. Earlier text versions ran on MS-DOS, which was also quite stable due to its simplicity.  

The development of the audio compression format MPEG-1 Audio Layer 3, more commonly referred to as MP3,  provided the breakthrough in reducing traditionally large digital music files to much smaller compressed files without appreciable quality loss and thus being able to store vast quantities of MP3 encoded music on computer hard drive virtually signaling the end of large reel-to-reel tapes.  The MP3 audio-specific format  was designed by the Moving Picture Experts Group, a group formed by several teams of engineers at Fraunhofer IIS in Erlangen, Germany, AT&T-Bell Labs in Murray Hill, New Jersey, Thomson-Brandt Co.  and others.  It quickly became the de facto standard for digital audio compression and was approved as an standard in 1991.

Scheduling was an important advance in automation systems, allowing for exact timing. Some systems use GPS satellite receivers to obtain exact atomic time, for perfect synchronization with satellite-delivered programming. Automation systems are also more interactive than ever before with digital audio mixing consoles, and can even record from a telephone hybrid to play back an edited conversation with a telephone caller. This is part of a system's live-assist mode.

The use of automation software and voice tracks to replace live DJs is now the standard in radio broadcasting, done by many Internet radio and adult hits stations. Stations can even be voice-tracked from another city far away, now often delivering sound files over the Internet. In the U.S., this is a common practice under controversy for making radio more generic and artificial. Having local content is also touted as a way for traditional stations to compete with satellite radio, where there may be no radio personality on the air at all. The first PC hard-drive based automation system released to the public in America may have been Digital DJ, created by a Fort Worth, Texas company called The Management. 

Computer automation software does it all today.