Flash ROM

The Flash is a 256 kiB or 1 MiB non-volatile TSOP ROM chip and connected to the MCPX via a parallel bus on hardware revisions 1.0 to 1.4. The 256 kiB ROM on revision 1.6 is stored in the Xcalibur chip, not a flash chip, and is connected to the MCPX via the LPC bus (Xbox revision 1.6).

The Flash ROM is mapped at physical addresses 0xFF000000 to 0xFFFFFFFF (revision 1.0) or 0xFFFFFDFF (revisions 1.1 - 1.6). The 256 kiB or 1 MiB ROM is aliased throughout this 16 MiB address range. The ROM is commonly based in software at either 0xFFF00000 or 0xFFFC0000 as these are the addresses of the last alias for 1 MiB and 256 kiB respectively. Due to the MIST hack, Microsoft blocked the use of flash ROM in the range of the MCPX ROM (0xFFFFFE00 - 0xFFFFFFFF) for revisions 1.1 to 1.6. Once the MCPX ROM is hidden, accessing this memory range will freeze the system.

For the content of the Microsoft flash images see BIOS.