Models
While all iPods are roughly the same size and have the same capabilities, the design has undergone several revisions since it was first introduced to the market. There are four distinct generations of iPods, commonly known as 1G, 2G, 3G, and 4G. (These designations are not related to the Power Macintosh G3, G4, or other Macintosh models.)
Within any generation of iPods, various models have been available with different sizes of hard drives, at different price points. During the third and fourth generations, three sizes of iPods have been on the market at any given time, priced at $299, $399, and $499. The least expensive comes with earphones, a FireWire cable, and a wall plug to recharge the iPod's internal battery. The other two models include all that along with a belt-clip carrying case, a wired remote control, and a docking cradle.
The iPod mini is a smaller unit available in various colors and is not considered a member of one of the "generations," though it was released between the 3G and 4G models.
First generation
First announced on October 23, 2001, the original iPod was available for $399 with a 5 GB hard drive. Critics panned the unit's price, but the iPod was an instant hit in the marketplace. A 10 GB version ($499) was announced in March 2002, and a 20 GB version in July (introduced at $499 with a price drop of $100 for the other two models).
The mechanical scroll wheel, the most distinctive feature of the iPod, was designed by Apple but developed by Synaptics, a firm that also developed the trackpad used by many laptops, including Apple's PowerBooks. The 1G iPod featured four buttons - Menu, Play/Pause, Back, and Forward - arranged around the circumference of the scroll wheel.
Second generation
The 2G iPods replaced the mechanical scroll wheel with a touch-sensitive, non-moving one (also made by Synaptics) which could detect the motion of the user's finger circling around it. The button in the center of the wheel and the buttons around the wheel were still mechanical. These iPods came with a wired remote control and belt-clip carrying case.
Third generation
On April 28, 2003, Steve Jobs introduced an "ultrathin" iPod series. These were slightly smaller than their predecessors, and their edges were more bevelled. Over the life of the 3G iPod series, models were available in 15GB, 20GB, 30GB, and 40GB sizes.
These iPods used a new kind of connector, longer and flatter than a typical Firewire plug. This allowed them to fit more easily into a docking cradle (which shipped with all but the least-expensive iPod, and was also available separately).
The 3G iPod featured touch-sensitive buttons located below the display. They would glow red for a few seconds when touched, allowing the iPod to be used more easily in the dark.
With the 3G iPods, Apple stopped shipping separate Mac and Windows versions of the unit. Instead, all iPods now shipped with their hard drives formatted for Macintosh use; on the included CD-ROM was a Windows utility which could reformat them for use with a Windows PC. These iPods also introduced the ability to be used with a USB2 connection (the USB adapter cable was sold separately).
When purchased through the online Apple Store, the iPod featured custom engraving: two lines of text could be laser-engraved on the back (for an additional charge).
iPod mini
In January 2004, Apple introduced a smaller variation, the iPod mini. With 4 GB of storage and a price of $249 USD (which was only $50 below the 15GB iPod), it was panned by critics for being too expensive; but once again it was proven by its overwhelming popularity, and Apple Stores had difficulty keeping them in stock.
The iPod mini moves the buttons to the scroll wheel itself. Pressing an edge of the wheel clicks it like a button; hence, the new wheel is known as a "click wheel." Another notable distinction is that the iPod mini is available in a choice of five colors of anodized aluminum.
Fourth generation
In July 2004, the fourth generation of iPod was released. In a new publicity route, Steve Jobs announced it by being the subject of a front-page article in Newsweek magazine.
The most obvious difference between the 4G iPod and its predecessors is the introduction of the click wheel design from the iPod mini. The 4G iPod is slightly smaller, and it introduces the ability to charge the battery over a USB connection. It also offered larger capacities at the same price points; the 20GB unit cost $299 USD and the 40GB unit cost $399 USD.
Apple claims that updated software in the new iPod allows it to use the battery more efficiently and increase battery life to 12 hours, and minor changes such as the addition of a "Shuffle Songs" item on the top-level menu make it more convenient for users. There have been complaints from users of earlier iPods that the software improvements should be made available for previous models as well, but so far Apple has not addressed this.
The fourth generation iPod comes bundled with cables to connect it to FireWire and USB ports.
On October 28, 2004, the iPod Photo was released in 40GB and 60GB sizes with color displays and the ability to store and show photographs. Less than a month later it was renamed the "iPod photo", with the second word not capitalized.
On the same day, the iPod Special Edition U2 was also released. It is black with a red click wheel (the colours of U2's upcoming album, How to Dismantle an Atomic Bomb) and features the signatures of U2 band members engraved on the back, but otherwise is identical to 4G iPods. It comes with an iTunes Music Store coupon redeemable for $50 off the price of "The Complete U2," a "digital boxed set" featuring 400 tracks of U2 music.
Future
If the U2 Special Edition iPod is successful, it is likely that additional custom iPods will be made available in the future, with new colors and new laser-engraved designs.
Various credible sources in the Apple computing world and in the financial sector have reported rumors of the development of a flash drive-based iPod. Such a unit would have a smaller capacity than current hard drive-based iPods, but might have a much lower price.
Persistent rumors, encouraged by the release of the iPod photo with its color display, also are that Apple will someday introduce an iPod with video-playing capability.
