Recently Apple has announced that it has sold 100 million iPods, a record number, in just five years since the device was introduced. But with the iPod line-up reaching maturity, and so many of them already in the hands of customers, just how many more can Apple sell? Already some analysts are saying that the sales are softening.

Despite the record sales of the iPod, the market for portable music players is still large. In fact, analyst at JMP Securities think that the market is so large that the company will have no problems eclipsing the 350 million unit sales milestone achieved by Sony with its Walkman players during the 80's and 90's before the first real signs of fizzle set in.

"During Sony's 15-year reign with the Walkman, the company sold over 350 million units, and we believe that Apple's addressable market over time will exceed this number given the upgrade and replaceable nature of iPods as well as the overriding trend of consumers' increasing use of digital media," wrote Ingrid Ebeling in a research note distributed to JMP Securities clients. "The net takeaway is that this is a product category that is far from saturated, and we believe well over 500 million units will be sold before the product category hits maturation."

As new technologies come in and prices for the old ones drop, the iPods will continue their reign. Apple has showed that they know how to keep people interested, and they have proven that the only think that can kill the popular iPod is an even better iPod. If the iPhone is any indication of what the new top-range iPod will look like, there can be little doubt that Apple will continue to lead the market and sell record numbers of units. Even in the lower end of the market, Apple is competing in ore than just specifications, the new form factor of the Shuffle being a good example.