Devices in the iPod range are primarily digital music players, designed around a central click wheel although the iPod shuffle has buttons only.

The full-sized model stores media on an internal hard drive, while the smaller iPod nano and iPod shuffle use flash memory. Like many digital audio players, iPods can also serve as external data storage devices.

In addition to playing music, iPods with display screens can display calendars, contact information, and text files, and play a limited range of video games. Models introduced in 2004 include the ability to display photos and the fifth-generation iPod, introduced in 2005, can additionally play video files. In January 2007, Apple announced the iPhone, combining the features of a video-capable iPod with integrated mobile phone and mobile internet capabilities.

Apples iTunes software is used for transferring music (as well as photos, videos, games, contacts and calendars, for models that support those features). As a free jukebox application, iTunes stores a comprehensive library of music on the users computer and can play, burn, and rip music from a CD. It can also sync photos and videos.

History and Design:

The iPod came from Apple digital hub strategy, as the company began creating software for the growing market of digital devices being purchased by consumers. While digital cameras, camcorders and organizers had well-established mainstream markets, the company found digital music players lacking in user interface design and decided to develop its own.

The name was proposed by Vinnie Chieco, a freelance copywriter, who (with others) was called by Apple to figure out how to introduce the new player to the public. As soon as Chieco saw a prototype for the player he thought of the movie 2001: A Space Odyssey and the phrase: "Open the pod bay door, Hal!", which refers to the white EVA Pods of the Discovery One spaceship. At that time "iPod" was a name that Apple registered for Internet kiosks, but never put to use.

Apple hardware engineering chief Jon Rubinstein assembled a team of engineers to design it, including Tony Fadell, Stan Ng and Jonathan Ive. Additionally, Sparkfactor Design has designed some of the iPod hardware from 2002-2004. They developed the product in less than a year and it was unveiled on October 23, 2001. CEO Steve Jobs announced it as a Mac-compatible product with a 5 GB hard drive that put "1000 songs in your pocket."

Uncharacteristically, Apple did not develop the iPods software entirely in-house. Instead, Apple began with PortalPlayer reference platform which was based on 2 ARM cores. The platform used rudimentary software running on a commercial microkernel embedded operating system. PortalPlayer had previously been working on an IBM-branded MP3 player with Bluetooth headphones. Apple contracted another company, Pixo, to help design and implement the user interface, under the direct supervision of Steve Jobs.

Once established, Apple continued to refine the software look and feel. Starting with the iPod mini, the Chicago font (once used on early Macintosh computers) was replaced with Espy Sans, which was originally used in eWorld and Copland. Later iPods switched fonts again to Podium Sans, a font similar to Apple corporate font Myriad. The iPods with color displays then adopted some Mac OS X themes like Aqua progress bars, as well as brushed metal in the lock interface.

User interface:

Apple focused its development on the iPod's unique user interface and its ease of use, rather than on technical capability. The iPod is currently the world's best-selling range of digital audio players and its worldwide mainstream adoption makes it one of the most popular consumer brands. Some of Apple's design choices and proprietary actions have, however, led to criticism and legal battles.

The iPods with color displays use high quality anti-aliased graphics and text, with sliding animations. These iPods have five buttons and the newer generations have the buttons integrated into the click wheel an innovation which gives an uncluttered, minimalistic interface.

The buttons are:

Menu to traverse backwards through the menus, and toggle the backlight on older iPods when held

Center to select a menu item

Play / Pause which doubles as an off switch when held

Fast Forward (When held)/ Skip Forward

Fast Reverse (When held)/ Skip Backwards

The operations such as scrolling through menu items and controlling the volume are performed by using the click wheel in a rotational manner. These iPods also have a Hold switch at the top, which prevents accidental button presses.

Newer iPods automatically pause playback when the headphones are unplugged from the headphone jack, but playback does not resume when the headphones are re-inserted.

However, in newer iPods (excluding iPod shuffles), when the headphones are re-inserted into the headphone jack when the iPod is asleep, the iPod will automatically wake up to the last screen viewed before going to sleep. An iPod that has crashed or frozen can be reset by switching 'Hold' on then off, then holding Menu and Center (Menu and Play on the 3G iPod) for 6 seconds.

The iPod shuffle does not use a click wheel and instead has five buttons positioned differently to the larger models. It has a Play / Pause button in the center, surrounded by four buttons: Volume Up / Down and Skip Forward / Backwards. This button arrangement is shared by the Apple Remote (which ships with all Apple computers with Front Row and the Universal Dock).