Jonathan Bare has peaked on the Apple TV harddrive (whilst replacing it with a larger one), and noticed the software running on Apple TV has been dubbed by Apple as “Backrow”:

The interface that runs Apple TV is, in part at least, apparently called BackRow and can be found in the OSBoot/System/Library/PrivateFrameworks/BackRow.framework. All of the imagery and the Intro.mov startup movie for the Apple TV can be found in the Resources directory at that location.

You can also find the background logo for the boot at OSBoot/System/Library/BootLogo.png.