Some built-in games are available, including Brick (a clone of Breakout), Parachute, Solitaire, and iPod Quiz. In March 2002, Apple added limited PDA-like functionality: text files can be displayed, while contacts and schedules can be viewed and synchronized with the host computer.
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Custom firmware has also been developed such as Rockbox (up to 6G - 6G requires emCORE) and iPodLinux (up to 5G) which offer open-source alternatives to the standard firmware and operating system. For example, an iPod could spin its hard disk up once and copy approximately 30 MB of upcoming songs into RAM, thus saving power by not requiring the drive to spin up for each song. A portion of the RAM is used to hold the iPod OS loaded from firmware, but the majority of it serves to cache songs from the storage medium. Each iPod also has 32 MB of RAM, although the 60GB and 80GB fifth generation, and the sixth-generation models have 64 MB. An additional NOR flash ROM chip (either 1 MB or 512 KB) contains a bootloader program that tells the device to load its OS from the storage medium. The iPod's operating system is stored on its dedicated storage medium. Play / Pause: this doubles as an off switch when held.
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