NVIDIA MCPX (labeled MCP1 on the die) southbridge from the original Xbox. Alleged to contain the secret boot ROM.
Made by a 150 nm 7-metal process by TSMC according to http://amo.net/NT/02-15-01XBOX.html.
From preliminary die inspection, stack-up looks to be:
Size is approximately 5300 x 5300 μm (28.1 mm2)
Mask rev markings. Looks very similar to the GeForce 2 MX suggesting the two are made on the same, or nearly same, process. This is a little odd since the GeForce 2 was supposed to be 180 nm and sources list this chip as 150.
Classic NVIDIA diagonal bond pads
Possible boot ROM?
Multi-focus stack down interconnect. Looks like 3 vertical, 3 horizontal layers plus M1 (not visible in this view).
Closeup near bottom right showing cell sizes