On February 19, 2007, XM and Sirius announced a merger that will be finalized in late 2007 or early 2008. Until the merger is completed, each company will provide the unique programming listed in this article.
XM and Sirius originate their programming from digital broadcast centers that house dozens of individual recording studios. Each broadcast center stores its music digitally on huge hard disk arrays. XM's facility in Washington, DC, has approximately 96 terabytes of storage capacity -- enough to hold more than 2 million songs. The SIRIUS studios in mid-town Manhattan have similar storage capacity.
Both companies also maintain large collections of CDs to augment their digital libraries. They also retransmit programming that originates elsewhere, such as news, sports, and comedy channels.
To create a program for broadcast, a programmer or DJ sits behind a computer and simply points and clicks at the songs he wants to play. The music is then queued to play directly from the hard disk storage system at the scheduled time.
All of the music stored digitally also includes informational tags -- the song title and the artist. This information is encoded in a digital data stream that accompanies the digital music stream. When you listen to a song on XM or SIRIUS, you view this track information on your satellite receiver's multi-line LCD display.
The digital music broadcast via satellite is compressed to fit within the available bandwidth. This digital compression sometimes affects the audio quality, most notably on non-music channels. The resulting audio sounds more like FM radio than CD, but is adequate for in-car listening.
Michael Miller is a writer and commentator on technology and digital lifestyle topics. 
