iPod is a brand of portable media players designed and marketed by Apple and launched in October 2001. The line-up currently consists of the original style hard drive-based flagship iPod classic, the iPhone-like iPod touch, the mid-level video-capable iPod nano, and the low-end screenless iPod shuffle. Former products include the compact iPod mini (replaced by the iPod nano) and the high-end spin-off iPod photo (re-integrated into the main iPod classic line). The current iPod classic models store media on an internal hard drive, while all other current models use flash memory to enable their smaller size. As with many other digital music players, iPods can also serve as external data storage devices.

Apple's iTunes software is used to transfer music to the devices. As a jukebox application, iTunes stores a music library on the user's computer and can play, burn, and rip music from a CD. It also transfers photos, videos, games, and calendars to those iPod models that support them. Apple focused its development on the iPod's unique user interface and its ease of use, rather than on technical capability. As of September 2007, the iPod had sold over 110 million units worldwide (stated in "The Beat Goes On" conference) making it the best-selling digital audio player series in history.

iPod came from Apple's digital hub strategy, when the company began creating software for the growing market of digital devices being purchased by consumers. Digital cameras, camcorders and organizers had well-established mainstream markets, but the company found existing digital music players "big and clunky or small and useless" with user interfaces that were "unbelievably awful," so Apple decided to develop its own. Apple's hardware engineering chief, Jon Rubinstein, assembled a team of engineers to design it, including Tony Fadell, hardware engineer Michael Dhuey, and design engineer Jonathan Ive, with Stan Ng as the marketing manager. The product was developed in less than a year and 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 iPod's software entirely in-house. Apple instead used PortalPlayer's reference platform which was based on 2 ARM cores. The platform had 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's look and feel. Starting with iPod mini, the Chicago font was replaced with Espy Sans. Later iPods switched fonts again to Podium Sans — a font similar to Apple's corporate font Myriad. iPods with color displays then adopted some Mac OS X themes like Aqua progress bars, and brushed metal in the lock interface. In 2007, Apple modified the iPod interface again with the introduction of the sixth-generation iPod classic and third-generation iPod nano by changing the font to Helvetica, and in most cases, splitting the screen in half by displaying the menus on the left and album artwork, photos, or videos on the right (whichever was appropriate for the selected item).

The name iPod 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. After Chieco saw a prototype, 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. Joseph N. Grasso of New Jersey had originally listed an "ipod" trademark with the U.S. Patent and Trademark Office in July 2000 for Internet kiosks. The first ipod kiosks had been demonstrated to the public in New Jersey in March 1998, and commercial use began in January 2000. The trademark was registered by the USPTO in November 2003, and Grasso assigned it to Apple Computer, Inc. in 2005.

iPod can play MP3, AAC/M4A, Protected AAC, AIFF, WAV, Audible audiobook, and Apple Lossless audio file formats. The iPod photo introduced the ability to display JPEG, BMP, GIF, TIFF, and PNG image file formats. Fifth and sixth generation iPod classics, as well as third generation iPod nanos, can additionally play MPEG-4 (H.264/MPEG-4 AVC) and QuickTime video formats, with restrictions on video dimensions, encoding techniques and data-rates. Originally, iPod software only worked with Macs; however, starting with the second generation model, iPod software worked with Windows and Macs. Unlike most other media players, Apple does not support Microsoft's WMA audio format — but a converter for WMA files without Digital Rights Management (DRM) is provided with the Windows version of iTunes. MIDI files also cannot be played, but can be converted to audio files using the "Advanced" menu in iTunes. Alternative open-source audio formats such as Ogg Vorbis and FLAC are not supported without installing custom firmware onto the iPod.

The iPod is associated with one host computer. Each time an iPod connects to its host computer, iTunes can synchronize entire music libraries or music playlists either automatically or manually. Song ratings can be set on the iPod and synchronized later to the iTunes library, and vice versa.

iPods with color displays use anti-aliased graphics and text, with sliding animations. Classic iPods have five buttons and the later generations have the buttons integrated into the click wheel — an innovation which 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. iPod shuffle does not have a click wheel and instead has five buttons positioned differently from the larger models. iPod touch uses no buttons for any of these functions, instead relying on the same Multi-touch input style as the iPhone.

The iTunes Store is an online media store run by Apple and accessed via iTunes. It was introduced on April 29, 2003 and it sells individual songs, with typical prices being US $0.99, AU $1.69 (inc. GST), NZ $1.79 (inc. GST), €0.99 (inc. VAT), or £0.79 (inc. VAT) per song. Since no other portable player supports the DRM used, only iPods can play protected content from the iTunes store. The store became the market leader soon after its launch and Apple announced the sale of videos through the store on October 12, 2005. Full-length movies became available on September 12, 2006.

Purchased audio files use the AAC format with added encryption. The encryption is based on the FairPlay DRM system. Up to five authorized computers and an unlimited number of iPods can play the files. Burning the files onto an audio CD, then re-compressing can create music files without the DRM, although this results in reduced quality. The DRM can also be removed using third-party software. However, in a deal with Apple, EMI began selling DRM-free, higher-quality songs on the iTunes Stores, in a category called "iTunes Plus." While individual songs were made available at a cost of US$1.29, 30¢ more than the cost of a regular DRM song, entire albums were available for the same price, US$9.99, as DRM encoded albums. On October 17, 2007, Apple lowered the cost of individual iTunes Plus songs to US$.99 per song, the same as DRM encoded tracks.

iPods cannot play music files from competing music stores that use rival-DRM technologies like Microsoft's protected WMA or RealNetworks' Helix DRM. Example stores include Napster and MSN Music. RealNetworks claims that Apple is creating problems for itself by using FairPlay to lock users into using the iTunes Store. Steve Jobs has stated that Apple makes little profit from song sales, although Apple uses the store to promote iPod sales. However, iPods can also play music files from online stores that do not use DRM, such as eMusic or Amie Street.

On July 3, 2007, Universal Music Group decided not to renew their contract with the iTunes music store. Universal will now supply iTunes in an 'at will' capacity.

On September 5, 2007, at Apple's Media Event entitled "The Beat Goes On...", the company debuted the iTunes Wi-Fi Music Store which allows one to access the Music Store from either iPhone or the new WiFi-enabled iPod Touch and download songs directly to the device. When you next sync the device with iTunes, any purchased music is copied onto your iTunes Library.

With the exception of the iPod touch, all iPods can function as mass storage devices to store data files. If the iPod is formatted on a Mac OS X computer it uses the HFS+ file system format, which allows it to serve as a boot disk for a Mac computer. If it is formatted on Windows, the FAT32 format is used. With the advent of the Windows-compatible iPod, iPod's default file system switched from HFS+ to FAT32, although it can be reformatted to either filesystem (excluding the iPod shuffle which is strictly FAT32). Generally, if a new iPod (excluding the iPod shuffle) is initially plugged into a computer running Windows, it will be formatted with FAT32, and if initially plugged into a Mac running Mac OS X it will be formatted with HFS+.

Unlike many other MP3 players, simply copying audio or video files to the drive with a typical file management application will not allow iPod to properly access them. The user must use software that has been specifically designed to transfer media files to iPods, so that the files are playable and viewable. Aside from iTunes, several alternative third-party applications are available on a number of different platforms.

iTunes 7 and above can transfer purchased media of the iTunes Store from an iPod to a computer, provided that the DRM media is transferred to any of the five computers allowed for authorization with DRM media.

Media files are stored on the iPod in a hidden folder, together with a proprietary database file. The hidden content can be accessed on the host operating system by enabling hidden files to be shown. The audio can then be recovered manually by dragging the files or folders onto the iTunes Library or by using third-party software.

Originally, a FireWire connection to the host computer was used to update songs or recharge the battery. The battery could also be charged with a power adapter that was included with the first four generations. The third generation began including a dock connector, allowing for FireWire or USB connectivity. This provided better compatibility with PCs, as most of them did not have FireWire ports at the time. However, the device could not be charged over USB, so the FireWire cables were nonetheless needed to connect to the AC adapter. The dock connector also brought opportunities to exchange data, sound and power with an iPod, which ultimately created a large market of accessories, manufactured by third parties such as Belkin and Griffin. The second generation iPod shuffle uses a single 3.5 mm jack which acts as both a headphone jack and a data port for the dock.

The iPod mini and the fourth generation iPod allowed recharging via USB and eventually Apple began shipping iPods with USB cables instead of FireWire, although the latter was available separately. As of the first generation iPod nano and the fifth generation iPod classic, Apple discontinued using FireWire for data transfer and made a full transition to USB 2.0, due to its widespread adoption. FireWire was then usable for recharging only.

Many accessories have been made for the iPod. A large amount are made by third party companies, although many, such as iPod Hi-Fi, are made by Apple. This market is sometimes described as the iPod ecosystem. Some accessories add extra features that other music players have, such as sound recorders, FM radio tuners, wired remote controls, and audio/visual cables for TV connections. Other accessories offer more unique features like the Nike+iPod pedometer and the iPod Camera Connector. Other notable accessories include external speakers, wireless remote controls, protective cases/films and wireless earphones. Among the first accessory manufacturers were Griffin Technology, Belkin, JBL, Bose, Monster Cable, and SendStation.

The white earphones (or "earbuds") that ship with all iPods have become symbolic of the brand. Advertisements feature them prominently, often contrasting the white earphones (and cords) with people shown as dark silhouettes. The original earphones came with the first generation iPod. They were revised to be smaller after Apple received complaints of the earbuds being too large. The revised earphones were shipped with second through early fifth generation iPods, the iPod mini, and the first generation nanos The earbuds were revised again in 2006, featuring an even smaller and more streamlined design. This third type was shipped with late fifth generation iPods and the second generation nanos. All first generation iPod shuffles and the second generation up until January 30, 2007 (when color models were introduced) had the second kind; those that shipped after that date had the third kind.

In 2005, New York's Metropolitan Transportation Authority placed adverts on the subways warning passengers that "Earphones are a giveaway. Protect your device", after iPod thefts on the subway rose from zero in 2004 to 50 in the first three months of 2005.

BMW released the first iPod automobile interface, allowing drivers of newer BMW vehicles to control their iPod using either the built-in steering wheel controls or the radio head-unit buttons. Apple announced in 2005 that similar systems would be available for other vehicle brands, including Mercedes-Benz, Volvo, Nissan, Alfa Romeo, Ferrari, Acura, Audi, Honda, Renault and Volkswagen. Scion offers standard iPod connectivity on all their cars.

Some independent stereo manufacturers including JVC, Pioneer, Kenwood, Alpine, Sony, and Harman Kardon also have iPod-specific integration solutions. Alternative connection methods include adaptor kits (that use the cassette deck or the CD changer port), audio input jacks, and FM transmitters such as the iTrip — although personal FM transmitters are illegal in some countries. Many car manufacturers have added audio input jacks as standard.

Beginning in mid-2007, four major airlines, United, Continental, Delta, and Emirates reached agreements to install iPod seat connections. The free service will allow passengers to power and charge their iPod, and view their video and music libraries on individual seat-back displays. Originally KLM and Air France were reported to be part of the deal with Apple, but they later released statements explaining that they were only contemplating the possibility of incorporating such systems.

Each new generation usually has more features and refinements while typically being smaller and lighter than its predecessor. Notable changes include the touch-sensitive click wheel replacing the mechanical scroll wheel, use of color displays, and flash memory replacing hard disks. Discontinued models include the first five generations of the full-sized iPod, both generations of the iPod mini, the first generation of the shuffle, and the first two generations of the nano.

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, and started selling iPods that included both Macintosh and Windows versions of iTunes so that they could be used with either platform.

In December 2002, Apple unveiled its first limited edition iPods, with either Madonna’s, Tony Hawk’s, or Beck’s signature or No Doubt's band logo engraved on the back for an extra US$50.[27] On October 26, 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 October 13, 2006, Apple released a special edition 4 GB red iPod nano as part of the 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 September 5, 2007, Apple also added a 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.

iPod batteries are not designed to be removed or replaced by the user, although some users have been able to open the case themselves, usually following instructions from third-party vendors of iPod replacement batteries. Compounding the problem, Apple initially would not replace worn-out batteries. The official policy was that the customer should buy a refurbished replacement iPod, at a cost almost equivalent to a brand new one. All lithium-ion batteries eventually lose capacity during their lifetime (guidelines are available for prolonging life-span) and this situation led to a small market for third-party battery replacement kits.

Apple announced a battery replacement program on November 14, 2003, a week before a high publicity stunt and website by the Neistat Brothers. The initial cost was US$99, and it was lowered to US$59 in 2005. One week later, Apple offered an extended iPod warranty for US$59. For the iPod nano, soldering tools are needed because the battery is soldered onto the main board. Fifth generation iPods have their battery attached to the backplate with adhesive.

The third generation iPod had a weak bass response, as shown in audio tests.The combination of the undersized DC-blocking capacitors and the typical low-impedance of most consumer headphones form a high-pass filter, which attenuates the low-frequency bass output by up to 10 dB. Similar capacitors were used in the fourth generation iPods.The problem is reduced when using high-impedance headphones and is completely masked when driving high-impedance (line level) loads. The first generation iPod shuffle uses a dual-transistor output stage rather than a single capacitor-coupled output, and does not exhibit reduced bass response for any load.

iPods have been criticized for their short life-span, fragile hard drives, and planned obsolescence.A 2005 survey conducted on the MacInTouch website found that the iPod had an average failure rate of 13.7%. It concluded that some models were more durable than others. In particular failure rates for iPods employing hard drives was usually above 20% while those with flash memory had a failure rate below 10%, indicating poor hard drive durability. In late 2005, many users complained that the surface of the first generation iPod nano can become scratched easily, rendering the screen unusable. A class action lawsuit was also filed. Apple initially considered the issue a minor defect, but later began shipping these iPods with protective sleeves.

On June 11, 2006, the British newspaper Mail on Sunday reported that iPods are mainly manufactured by workers who earn no more than US$50 per month and work 15-hour shifts. Apple investigated the case with independent auditors and found that, while some of the plant's labour practices met Apple's Code of Conduct, others did not: Employees worked over 60 hours a week for 35% of the time, and worked more than six consecutive days for 25% of the time.

Apple's manufacturer — which initially denied the abuses — promised to disallow working more hours than the Code allowed. Apple hired a workplace standards auditing company, Verité, and joined the Electronic Industry Code of Conduct Implementation Group to oversee the measures. On December 31, 2006, workers at the Taiwanese factory (owned by Foxconn) formed a union. The union is affiliated with the All-China Federation of Trade Unions.

In 2005, Apple Computer faced two lawsuits claiming patent infringement by the iPod and its associated technologies: Advanced Audio Devices claimed the iPod breached its patent on a "music jukebox", while a Hong Kong-based IP portfolio company called Pat-rights filed a suit claiming that Apple's FairPlay technology breached a patent issued to inventor Ho Keung Tse. The latter case also includes the online music stores of Sony, RealNetworks, Napster, and Musicmatch as defendants.

Apple's application to the United States Patent and Trademark Office for a patent on "rotational user inputs", as used on the iPod's interface, received a third "non-final rejection" (NFR) in August 2005. Also in August 2005, Creative Technology, one of Apple's main rivals in the MP3 player market, announced that it held a patent on part of the music selection interface used by the iPod, which Creative dubbed the "Zen Patent", granted on August 9, 2005. On May 15, 2006, Creative filed another suit against Apple with the United States District Court for the Northern District of California. Creative also asked the United States International Trade Commission to investigate whether Apple was breaching U.S. trade laws by importing iPods into the United States.

On August 24, 2006, Apple and Creative announced a broad settlement to end their legal disputes. Apple will pay Creative US$100 million for a paid-up license, to use Creative's awarded patent in all Apple products. As part of the agreement, Apple will recoup part of its payment, if Creative is successful in licensing the patent. Creative then announced its intention to produce iPod accessories by joining the Made for iPod program.

iPods have won several awards ranging from engineering excellence, to most innovative audio product, to fourth best computer product of 2006. iPods often receive favorable reviews; scoring on looks, clean design, and ease of use. PC World says that iPods have "altered the landscape for portable audio players". Several industries are modifying their products to work better with both the iPod and the AAC audio format. Examples include CD copy-protection schemes, and mobile phones, such as phones from Sony Ericsson and Nokia, which play AAC files rather than WMA. Microsoft's Zune device also supports AAC and it has adopted a similar closed DRM model used by iPods and the iTunes Store, despite Microsoft previously marketing the benefits of choice with their PlaysForSure initiative. Podcasts and download charts have also had mainstream adoption.

In addition to its reputation as a respected entertainment device, the iPod has also become accepted as a business device. Government departments, major institutions and international organisations have turned to the iPod as a delivery mechanism for business communication and training, such as the Royal and Western Infirmaries in Glasgow, Scotland where iPods are used to train new staff.