There are many reasons to like the iPod, but to me, the most compelling one is the scrollwheel. There's never been anything better for negotiating the prodigious amounts of music that we're lucky enough to be able to fit into our pockets these days. The scrollwheel has been through three iterations. The first one actually rotated; then there was the touch-sensitive one; and finally there's the clickable one found on the iPod Mini and fourth-generation iPod. I'd always assumed that this bit of design genius sprung from Apple's R&D labs, but, in fact, I discovered that a company called Synaptics, which primarily makes touchpads for laptops, actually perfected this little piece of navigational heaven, in accordance with Apple's stringent design requirements.

The Backstory
Although you probably haven't heard of the company before, there's a higher than 70 percent chance that the touchpad on any notebook you've ever used was made by Synaptics. You probably noticed that when you moved your finger more quickly across the touchpad, the mouse moved more quickly across the screen. The iPod's scrollwheel works via the same principle, which is one reason it's so effective at blasting through long song lists.

Synaptics' knack for navigation seems to have caught on, because Creative tapped Synaptics for its first touch-sensitive player, the Creative Zen Touch, and HP's new iPaq Pocket PC handheld has a "NavPoint" from the company as well.

Synaptics custom designs each of its touchpads based on a client's needs. Let's take a look at the evolution of the scrollwheel to see how those needs have changed, ultimately creating better and better iPods.

Scrollwheel: The First Generation

To the right is the original scrollwheel, designed by Apple, which physically rotated and was not touch-sensitive. I'm partial to the motionless designs that came later, but I know a couple of people who still prefer this one, because they like the feeling of the control moving with their finger (as opposed to their finger rubbing a stationary scrollwheel).

After the first iPod caught on, Apple started thinking of ways to improve it. Here's where Synaptics comes into the equation. The company had already worked with Apple on its iBooks, and so when Apple was looking for a way to make the iPod thinner and lighter, it elected to try out a touch-sensitive design from Synaptics. Aside from enabling a more pocket-friendly iPod, the new design also didn't permit any potential grime to gum up the scrollwheel's inner workings (I've never heard of this happening, but apparently it was a concern). To the right, you can see the original iPod and Synaptics' touch-sensitive scroll wheel that replaced Apple's mechanical design.

The Plot...Thins

Apple considered the touch sensitive scrollwheel an improvement over the original design, but decided to migrate the playback control buttons from around the scrollwheel to above it, in a straight line. The Synaptics scrollwheel itself maintained that cool "lightning zap" appearance (I almost want to figure out how to remove the plastic to expose it), while adding four touch-sensitive buttons. Initially, these buttons went over well with consumers, but some users complained that the buttons didn't always work. To me, it's a matter of design; human fingers want to know that they've pressed a button, rather than relying on visual feedback to confirm that the desired action has been accomplished.

Click, There It Is

When Apple designed the iPod Mini, those buttons had to go, because there simply wasn't enough real estate on the front of the device. The solution was a clever one. By making the scrollwheel clickable, it performs two functions: It allows for song-scrolling, and it provides playback control. To me, this was a huge design improvement, because the 2G/3G iPods' touch-sensitive playback controls didn't offer any feedback to the finger. With the clickable scrollwheel, when you depress the wheel, you get physical feedback that let's you know that you've pushed a button. This new version worked so well that Apple decided to build it into the full-sized fourth-generation iPod, doing away with buttons altogether.

Well, there you have it--the backstory behind and the evolution of the iPod scrollwheel. Synaptics wasn't offering its technology to any other MP3 player companies until recently, and it still doesn't offer the round version found on the iPod to anyone but Apple. However, as mentioned above, the company made a straightened-out version of it for Creative's Zen Touch, which evidently doesn't violate whatever agreement Synaptics has with Apple. It makes a bit more sense conceptually, since song lists run up and down instead of in circles, but the scrollwheel lets you scroll faster, because your finger can go around continuously instead of returning to the top of the strip. To make the Zen Touch even more competitive with the iPod, I recommended to Creative that it implement a new feature that would scroll down one screen, which is the same theory behind clicking down a Web page or Word document. This might make it easier to find what you're looking for without being dizzied by all that text whizzing past you.

As for Apple's latest scrollwheel, I'm plumb out of ideas for how it could be improved. If you have some of your own, kindly let me know.

Note: This story has been altered since its original publication to correct an error regarding the original, mechanical scrollwheel.