Firmware

A firmware is an IPSW file that contains everything needed to run the core operating system, iOS. This page lists all the firmwares Apple has released to the general public. Beta builds have also been released, but require an Apple Developer account to acquire. To check for updates, iTunes contacts ax.phobos.apple.com.edgesuite.net.

Apple TV
Apple TV firmwares have two different version and build numbers, which can lead to confusion when referencing them. As such, the internal build number is the best way to refer to a specific firmware.
 * The "Marketing"/"Displayed" columns are what is reported on the Apple TV's "About" screen
 * The "Internal" column refers to the  and   keys in the IPSW's