January 28, 1999 is a day which wrote emulation history. UltraHLE was released, the first succesful Nintendo 64 emulator. What many thought of as impossible was achieved by UltraHLE as the first (and only) release was able to properly play many popular titles, including Super Mario 64 and Zelda: Ocarina of Time.
High Level Emulation
UltraHLE also pioneered a new approach to emulation. Instead of trying to emulate all components of of a game console (such as CPU) as accurately as possible, it tries to recognize what a game is trying to achieve (like playing a sound) and emulates that function.
This is known as High Level Emulation (HLE) and it is what makes UltraHLE and other emulators which have incorperated (some of) this technology so relatively fast. It has a drawback however. If game does things a little differently the emulator won't be able to accuratly guess what the game is doing, which means the game may not play properly.
Bacause of this limitation HLE emulators usually only work well with the games they have been specifically optimized for. Because there was never an update to UltraHLE, this would have been a major limiting factor for it's success as newer games probably wouldn't run on it. Fortunately most of the information on how UltraHLE should treat and emulate games was stored in a seperate INI file.
Certain people started to experiment with UltraHLE and expanded and enhanced this INI file, which allows UltraHLE play a lot more games. As such, be sure to download an updated INI file if you want to try UltraHLE.
The reaction of the general public to UltraHLE was so intense that the creators of UltraHLE discontinued the emulator only a few hours after it's initial release. One of the authors, RealityMan, later continued the project again and started working on a new version of UltraHLE.
Unfortunately, there are many people who believe that emulators exist solely for piracy and that emulator authors are their slaves. The comments and "demands" received from these people combined with legal pressure from Nintendo forced RealityMan to decide to completely abandon UltraHLE and emulation. In other words, there will never be a new version.
There is one major limitation of UltraHLE which has probably plagued almost everyone since it's release. It was designed to operate exclusively on 3DFX Voodoo 1 and 2 secondary 3D cards. By default it will not run on any kind of other video card because it can't find the "Glide" drivers it needs (specifically the file GLIDE2X.DLL).
Of course a solution was designed for this. The Glide drivers can be emulated by using a "Glide Wrapper". These wrappers redirect the commands issued by UltraHLE to your video card, no matter which one you are using (depending on which kind of wrapper you use).