The iPod line has been upgraded many times, and each significant revision is called a "generation". Only the most recent (highest numbered) generation and refurbished units of previous generations of the iPod line are available from Apple for each model (Classic, Nano, Shuffle, Touch). Each new generation usually has more features and refinements while typically being physically smaller and lighter than its predecessor, while usually (but not always) retaining the older model's price tag. Notable changes include the touch-sensitive click wheel replacing the mechanical scroll wheel, use of color displays, and flash memory replacing hard disks. The software bundled with the first generation iPod was Macintosh-only, so Windows users had to use third-party software like ephPod or XPlay to manage their music. When Apple introduced the second generation of iPods in July 2002, they sold two versions, one that included iTunes for Macintosh users and another that included Musicmatch Jukebox for Windows users.

In October 2003, Apple released the Windows version of iTunes,[44] and started selling iPods that included both Macintosh and Windows versions of iTunes so that they could be used with either platform. Current iPods no longer ship with iTunes, which must be downloaded from Apple's website. In December 2002, Apple unveiled its first limited edition iPods, with Madonna's, Tony Hawk's, or Beck's signature or No Doubt's band logo engraved on the back for an extra US$50. I had seen the adverts on TV on how small the nano was but it wasn't until I held one in my hands that I fully understood how small and how impressive these MP3 players are. Weighing only 42grams and a mere 90m by 40m and only 6.9m thick (or thin) these little units are not going to fill your suitcase when you go on holiday. Ideal for putting in your pocket, wallet or purse you can take them anywhere, except the pool of course as they are not waterproofs. The small size does create concerns for me with my children though. They can easily get lost if not looked after and outside of the home could be easy prey to pickpockets or thieves so beware.

They come in two colours white and black and two memory sizes 2gb and 4gb, theses can hold 500 and 1000 songs respectively. For me this is more than enough songs but for those of you with large CD collections, who want to put their whole collection in one place, you may want to go for one the larger iPods. The colour screen looks excellent and shows easy navigation throughout, you can download your tunes into files, albums, types of music etc. My only concern with the screen was, I felt it may scratch easily and some of the cases that you can buy for the nano still leave the screen exposed. My concern is when you put your nano into your pocket or bag and catches something metal. I had heard on the news there had been issues with the early nanos, I still feel this could be an issue. The main control in the centre of the unit was more touch sensitive than I expected, I use my thumb to scroll the menu, but it wasn't long before it was easy as pie, if fact working really well with the gel case I had bought to protect it. The sound is excellent, I can't tell the difference between CDs and MP3s and I often think those who say they can, can't either. You can download your music from iTunes, a legal way of owning music.

They are impressively boxed also, where you open the box like a book and see your nano inside. However you do not get any form of charging your nano except for the computer leads that come with it. This means if you wish to take your nano away from your computer for a period of time you will need to buy a separate mains charger. Which of course is larger than the unit itself? My final conclusion is that this little unit is a fantastic move forward in the music player industry. I was impressed by the larger iPods that my friends had, but it wasn't until the appearance of the nano that I was suitably impressed to put my hand in pocket to make a purchase. And I haven't been let down. On 26 October 2004, Apple introduced a special edition of its fourth generation monochrome iPod, designed in the color scheme of the album How to Dismantle an Atomic Bomb by Irish rock band U2. It had a black case with a red click wheel and the back had the engraved signatures of U2's band members.

This iPod was updated alongside the iPod Photo and fifth generation iPod. On 13 October 2006, Apple released a special edition 4 GB red iPod Nano as part of the Product Red campaign. An 8 GB version was released three weeks later and both of them sold for the same price as the standard models. US$10 from each sale is donated to The Global Fund to Fight AIDS, Tuberculosis & Malaria. On 5 September 2007, Apple also added a Product Red iPod Shuffle model. They did not disclose how much will be donated to charity from this model. Apple also released Special Edition Harry Potter iPods to accompany the iPod Photo. These were engraved with the Hogwarts Crest on the back and were only available to purchasers of the Harry Potter audiobooks. They were updated when the fifth generation iPods were released, but were only available for a limited time. In 2007, a Cubismo special edition 2 GB silver iPod Nano was made available only in the former Yugoslav republics.