UltraHLE

UltraHLE is a discontinued emulator for the Nintendo 64. Emulating the Nintendo 64 (which was only three years old at the time) made it the first of the N64 emulators to run commercial titles at a playable frame rate on the hardware of the time, which drew Nintendo to seek legal action against the developers.

The Ultra High-level (UHLE) technique

Earlier emulators had sought to accurately emulate all low-level operations of a target machine; this worked well for consoles such as the Super NES and Genesis that were substantially simpler than the computer running the emulator.

HLE was done even before the UltraHLE emulator (to emulate the BIOS, and the SNES enhancement chips). But UltraHLE introduced aggressive optimization and time-savers which go beyond traditional HLE.

Co-authors Epsilon and RealityMan realized that since N64 games were programmed in C, they could intercept (the far fewer) C library calls rather than machine-level operations, and simply reimplement the libraries. Thus UltraHLE is an emulator that is partly implemented as a simulator, in contrast to projects such as MAME. However it paved the way for playable emulators of recent consoles that require considerable graphical computational power which could be simulated easily with available PC graphic cards.

The final implementation was written in C and used the Glide API, specific to 3dfx adapters. Due to the emulator's popularity, several Glide to DirectX translation utilities were made specifically for UltraHLE for non-3dfx video cards.

UltraHLE's high-level emulation had its drawbacks; at the time of its release it was able to emulate only approximately 20 games to a playable standard as it emulated and simulated only those calls required by those specific games; it was necessary to adapt the emulator for games that used different parts of the N64 hardware. Nevertheless it supported many more titles than other contemporaneous N64 emulation projects such as Project Unreality.