On 7 July 1994, the Fraunhofer Society released the first software MP3 encoder called l3enc. The filename extension <answer>.mp3</answer> was chosen by the Fraunhofer team on 14 July 1995 (previously, the files had been named .bit). With the first real-time software MP3 player WinPlay3 (released 9 September 1995) many people were able to encode and play back MP3 files on their PCs. Because of the relatively small hard drives back in that time (~ 500–1000 MB) lossy compression was essential to store non-instrument based (see tracker and MIDI) music for playback on computer.
What was the filename extension?
.mp3