The Xbox BIOS is the first code executed by the console’s CPU upon powering on. It initializes the hardware—including the Nvidia-based GPU and the custom Intel Pentium III processor—and enforces security checks before handing control over to the dashboard or a game disc. For xemu to achieve high compatibility and accuracy, it must replicate these initialization steps. Unlike some emulators that use "High-Level Emulation" (HLE) to rewrite BIOS functions in modern code, xemu utilizes "Low-Level Emulation" (LLE). This approach requires an authentic copy of the Xbox BIOS image to ensure that the virtualized environment behaves exactly like the physical hardware, particularly regarding memory management and hardware interrupts.
For a standard Xemu setup, you are looking for three specific file types, though the total number depends on the BIOS version: xbox bios files xemu