The Personal Jukebox (also known as PJB-100 or Music Compressor) was the first commercially sold hard disk digital audio player. Introduced in 1999, it preceded the Apple iPod, SanDisk Sansa, and other similar players. The design was developed by Compaq Research (SRC and PAAD groups) starting in May 1998. Compaq did not release the player themselves, but licensed the design to HanGo Electronics Co., Ltd. of South Korea. Compaq Research published a software development kit for the unit, which enabled users to develop tools, drivers and applications for different operating systems.