The Xbox has no initialized RAM. The MCPX ROM configures the L2 cache of the Pentium III CPU to act as temporary No-Eviction RAM. This provides a tiny scratchpad space for the stack and variables required to calculate decryption keys.
: To ensure your file is a valid 1.0 version (the most common and widely supported), verify its hash: d49c64cc903823467f677da729e88d0a it in a specific emulator? Required Files | xemu: Original Xbox Emulator xbox bios mcpx10bin work
To get a working emulation environment, you must pair the MCPX file with a compatible Flash ROM (BIOS). The Xbox has no initialized RAM