On Monday, Apple announced that it has sold 100 million iPods, an unprecedented success story in the portable music player market. Apple said that its iPod is "the fastest selling music player in history," an accolade that's apparently meant to place the device above previous-generation portable devices, such as Sony's Walkman. No matter how you measure it, the iPod is an unqualified success, and the dominant player in a market that's increasingly defined by Apple.

"At this historic milestone, we want to thank music lovers everywhere for making iPod such an incredible success," said Apple CEO Steve Jobs. "iPod has helped millions of people around the world rekindle their passion for music, and we're thrilled to be a part of that."

The iPod got off to a slow start when first introduced in 2001, thanks to exorbitant pricing and Macintosh-only compatibility. After Apple made the iPod available to Windows users, lowered its prices, expanded its model lineup, and introduced its iTunes Store, the iPod took off, eclipsing its competitors. Today, the iPod controls more than 90 percent of the portable music player market worldwide. There are currently three iPod models--the iPod shuffle, the iPod nano, and the iPod with video--on the market, and Apple intends to introduce an iPod derivative, the iPhone, by mid-2007.

Not coincidentally, Apple's iTunes service has also been phenomenally successful, and Apple noted that iTunes is the world's most popular online music, TV, and movie store. The company has sold more than 2.5 billion songs, 50 million TV shows, and 1.3 million movies through the service, although the movie selection is lacking because of limited support from the movie industry.

Apple's success in the digital media market has led to several unsuccessful attempts by its competitors over the years to unseat the iPod. The latest entry into the market is Microsoft's Zune, which first shipped in late 2006. The Zune has captured roughly 10 percent of the market for hard disk-based MP3 players, and is already the second best-selling portable music device behind the iPod with video. Microsoft said it will continue in its efforts to combat the iPod with new Zune models and functionality updates this year, although it's unclear whether the company can really do anything to offset Apple's tremendous success.