The iPod line's signature click wheel.iPods with color displays use anti-aliased graphics and text, with sliding animations. All iPods (except shuffle and touch) have five buttons and the later generations have the buttons integrated into the click wheel - an innovation that gives an uncluttered, minimalist interface. The buttons perform basic functions such as play, next track, etc. Other operations such as scrolling through menu items and controlling the volume are performed by using the click wheel in a rotational manner. The iPod Shuffle does not have a click wheel and instead has five buttons positioned differently from the larger models. The iPod Touch uses no buttons for any of these functions, instead relying on a multi-touch input style similar to that of the iPhone. The company had, back in the 1990's, invented a technology called FireWire, which is basically a tool for moving data between digital devices -- in large quantities, very quickly. Apple licensed this technology to various Japanese consumer electronics companies (which used it in digital camcorders and players) and eventually started adding FireWire ports to iMacs and creating video editing software.

This led to programs called iMovie, then iPhoto and then a conceptual view of the home computer as a ''digital hub'' that would complement a range of devices. Finally, in January 2001, iTunes was added to the mix. And although the next step sounds prosaic -- we make software that lets you organize the music on your computer, so maybe we should make one of those things that lets you take it with you -- it was also something new. There were companies that made jukebox software, and companies that made portable players, but nobody made both. What this meant is not that the iPod could do more, but that it would do less. This is what led to what Jonathan Ive, Apple's vice president of industrial design, calls the iPod's ''overt simplicity.'' And this, perversely, is the most exciting thing about it. Later he said: ''What's interesting is that out of that simplicity, and almost that unashamed sense of simplicity, and expressing it, came a very different product. But difference wasn't the goal. It's actually very easy to create a different thing. What was exciting is starting to realize that its difference was really a consequence of this quest to make it a very simple thing.'' Before Ive came to Apple, he worked independently, often on projects that never got out of the prototype phase; one working model would be made, and then it would sit on a shelf in his office. You can think of innovation as a continuum, and this phase is one end of it. The dreams and experiments that happen outside of -- and in a state of indifference toward -- the marketplace.

At the other end of the continuum are the fast followers, those who are very attuned to the marketplace, but are not particularly innovative. Before you even get to the surface of the iPod, you encounter what could be called its aura. The commercial version of an aura is a brand, and while Apple may be a niche player in the computer market, the fanatical brand loyalty of its customers is legendary. A journalist, Leander Kahney, has even written a book about it, ''The Cult of Mac,'' to be published in the spring. As he points out, that base has supported the company with a faith in its will to innovate -- even during stretches when it hasn't. Apple is also a giant in the world of industrial design.

The candy-colored look of the iMac has been so widely copied that it's now a visual cliché. But the iPod is making an even bigger impression. Bruce Claxton, who is the current president of the Industrial Designers Society of America and a senior designer at Motorola, calls the device emblematic of a shift toward products that are ''an antidote to the hyper lifestyle,'' which might be symbolized by hand-held devices that bristle with buttons and controls that seem to promise a million functions if you only had time to figure them all out. ''People are seeking out products that are not just simple to use but a joy to use.'' Moby, the recording artist, has been a high-profile iPod booster since the product's debut. ''The kind of insidious revolutionary quality of the iPod,'' he says, ''is that it's so elegant and logical, it becomes part of your life so quickly that you can't remember what it was like beforehand.'' Tuesday nights, Andrew Andrew's iParty happens at a club called APT on the spooky, far western end of 13th Street. They show up at about 10 in matching sweat jackets and sneakers, matching eyeglasses, matching haircuts. They connect their matching iPods to a modest Gemini mixer that they've fitted with a white front panel to make it look more iPodish. The iPods sit on either side of the mixer, on their backs, so they look like tiny turntables. Andrew Andrew changes into matching lab coats and ties.

They hand out long song lists to patrons, who take a number and, when called, are invited up to program a seven-minute set. At around midnight, the actor Elijah Wood (Frodo) has turned up and is permitted to plug his own iPod into Andrew Andrew's system. His set includes a Squarepusher song. Between songs at APT, each Andrew analyzed the iPod.

In talking about how hard it was, at first, to believe that so much music could be stuffed into such a tiny object, they came back to the scroll wheel as the key to the product's initial seductiveness. ''It really bridged the gap,'' Andrew observed, ''between fantasy and reality.'' They let someone else do the risky business of wild leaps, then swoop in behind with an offering that funnels some aspect of the innovation into a more marketable (cheaper? watered down? easier to obtain?) package -- and dominates. Fairly or not, the shorthand version of this in the technology world would have at one end of the continuum Xerox PARC, the famous R&D lab where all manner of bleeding-edge innovations (including some of the ''look and feel'' of the Mac) were researched but never developed into marketable products. And at the other end you'd have companies like Microsoft and Dell.