Microsoft Xbox Repair Manual page 70

Mod Chips
This is an overview and the terminology is targeted at someone with little or no experience.
The Xbox has a bios like a computer, a mod chip replaces that bios with another. Microsoft
decided to shut off many computer like features in the Xbox, lots of techie geeks noticed this and
found the keys to unlock them. Some modders are driven by greed and game copying, others use
the Xbox as a computer running Linux or an advanced DVD/video player, and some are working
on tivo like functionality. The Xbox being in terms of processing and graphics technology, the
most powerful console on the market makes it a great platform to expand.
Like a PC when an Xbox boots it accesses the bios, in Xbox terms TSOP chip. Many tasks are
performed including checking memory, video, presence of DVD, Hard Drive etc. Once these
tasks are complete it asks the hard drive to load the operating system.
Enter the Mod Chip, these are chips designed to perform the same functions as the normal TSOP
but are altered slightly, they are hardwired to the board and come in may configurations from 30
wires, or 9 wires to no wires at all to solder. They wedge their way in, and take over for the
standard bios and perform the functions for it.
One standard alteration in all aftermarket BIOS's is there is no longer a check for signed code.
Original games have a digital signature that is checked for accuracy, if this check fails the game
or application will not load. Loading a bios that does not do a signature check allows modders to
run unsigned code. For some this means they can allow their Xbox to play games that are burned
to CD's. In theory one can burn copies of games they own, make a backup and play the backup
and keep the original safely in its case.* More importantly you are able to use this to install Linux
on an Xbox, through the use of an altered bios you will be able to link your Xbox through a
network connection and upload files as necessary.
*I do not condone the illegal copying of games or circumvention of copy protection!!!!
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