Flash ROM
From xboxdevwiki
The Flash is a 256 kiB or 1 MiB non-volatile TSOP ROM chip and connected to the MCPX via the LPC bus.
The Flash ROM is mapped at 0xFFF00000 (if the ROM is 1 MiB; 0xFFFC0000, if the ROM is 256 kiB) into the but the Xbox kernel.
For the content of the Microsoft flash images see BIOS.