NEW YORK (CNNMoney.com) -- Apple's iPod celebrates its fifth birthday Monday, marking a milestone for the music player that not only reinvigorated the "other" computer maker but revolutionized the way people buy and listen to music.

When Apple CEO Steve Jobs introduced the first iPod on Oct. 23, 2001, he said: "With iPod, listening to music will never be the same again."

After dominating music downloads, Apple is moving into movies now.

Apple's stock has skyrocketed in the last 5 years, largely due to its dominance in the portable music player market.

Indeed, the iPod and Apple's iTunes music store have transformed the music business, sparking a new way for users to legally download music - and spurring a stunning rise in Apple stock.

Apple (up $0.43 to $79.42, Charts) shares, which traded around $9 five years ago, have risen nearly nine-fold since then.

iPod sales are still growing - shipments rose to 8.73 million in the latest quarter, up 35 percent from a year earlier- even though there's some serious competition out there now for the world's most popular digital music player.

Microsoft's (Charts) Zune is due to launch next month, in time for the holiday season. Rival SanDisk (Charts) has also rolled out products to battle the iPod Nano.

But Apple dominates retail sales of digital music players with more than 70 percent of the market, according to research firm Current Analysis.

In the process of transforming the digital entertainment space, Apple has raised questions about what type of company it is: a consumer electronics firm, a software company or a computer maker?

The Cupertino, Calif.-based firm doesn't appear to be as concerned with defining itself as one thing or another. Instead, Apple has been focused on driving growth for its various products.

So far, the strategy looks to be working.

Sales of iPods have helped fuel sales of its Mac computers, and analysts say the company is now more of a contender in the race against personal computer makers like Dell (Charts) and Hewlett-Packard (Charts).

But after five years of dizzying growth, Apple faces the challenge of keeping up the momentum.

It's also been caught up in the stock options backdating scandal that has hit hundreds of firms. And that's likely to hang over its head until the matter is resolved.

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