BIOS files are proprietary code owned by Microsoft. Distributing them online without permission is a violation of copyright. While owning an emulator is legal, downloading firmware you do not own is generally considered digital piracy .
, the leading Xbox 360 emulator, does not require a BIOS file . It is designed to run games without needing the original console's copyrighted system software. Xbox 360 Emulator 1.7.1 Bios Download