Emulation accuracy

How accurate the emulator is to the original hardware. Accuracy is most often achieved by tighter syncing. Less accuracy = less CPU power needed to emulate. More accuracy = more CPU power to emulate.

Levels

Low

• ZSNES

High

• Mednafen PSX

Cycle Accuracy

• bsnes
• Exodus
• CEN64

Circuit accuracy

Atari emulator that runs at 15fps on high end systems

http://sourceforge.net/projects/dice/

Controversy

There are basically two camps when it comes to the issue of accuracy. One side argues that as long as an emulator plays the majority of games at full speed on most computers and devices without obvious glitches, it does not matter how accurately it actually replicates the original hardware and its many quirks and functions. The faithfulness of the emulator to the console it is emulating comes second to its overall ability to play games. The other side argues that an emulator should ultimately strive to simulate the hardware as much as possible, as that is the only way to achieve as much compatibility as possible, as well as the only way to preserve the hardware. Thus, speed and scalability to most devices takes a backseat to accuracy to the real console, both for purposes of compatibility and preservation.

Even within the second camp, however, there is some disagreement as to just how much accuracy is actually needed. On most platforms, after obtaining a certain amount of accuracy, going further still requires an exponential growth in system requirements, the results of which may not be noticeable to the vast majority of users. Cycle accuracy in particular has been hotly debated in regards to its usefulness, due to how such an extreme level of accuracy requires a lot of extra processing power for relatively few gains in compatibility.

Further reading

http://arstechnica.com/gaming/2011/08/accuracy-takes-power-one-mans-3ghz-quest-to-build-a-perfect-snes-emulator/

http://tasvideos.org/EmulatorResources/NESAccuracyTests.html