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An emulator is '''accurate''' when an instruction given to both the program and the hardware results in both outputting the same result. That means accurate emulators produce much less audio and video glitches at the cost of more processing power needed. It's often achieved by using tighter synchronization.
Notable accuracy-centric emulators include [[Mesen]] (NES), [[Higanhigan]] (SNES), [[CEN64]] (N64) and [[Exodus]] (Sega Mega Drive) among others.
The more accurate an emulator is, the lesser deviations there is from real hardware behavior but the more demanding it is. Ironically, that aspect might at times be at odds with how authentic the experience is, when it introduces [[Input lag]]. A similar debate surrounds CRT shaders as well. Not to mention the hardware intensive nature of very accurate emulators for later consoles may be at odds with the emulator's usability, especially with the recent collapse of Moore's Law (in layman's terms, you can't just "buy a better PC" if semiconductor technology does not catch up fast enough with what it takes for accurate emulation that makes zero compromises for optimizing speed)
===Chip accuracy===
By simulating each logic chip on the board individually, this not only takes a tremendous amount of processing power or specialized hardware to run (as in, even emulating something from the 1970s on a chip accurate level would need AAA-level system requirements to run at a good speed), but it also requires an incredible amount of effort to make, and <u>it's also almost useless</u>. Although it is the only way to achieve ''true'' hardware simulation, cycle accurate emulation can already achieve virtually indistinguishable accuracy from the real hardware, aside from a very negligible set of edge cases. In addition, cycle-accurate emulators have much lower system requirements and programming difficulty. The only chip accurate emulators that are currently usable run on Field Programmable Gate Arrays, or FPGAs[[FPGA]]s, which are essentially custom programmable chips. Machines dedicated to this type of emulation exist, such as the Analogue NT Mini by kevtris or the RetroUSB AVS by bunnyboy. Other examples of chip accurate emulation can be found in flash carts such as the SD2SNES, where various add-on chips are emulated on the included FPGA.
===DICE===
While it may be theoretically possible to have a 100% perfect emulator, that feat is very rare (if not nearly impossible), even for some highly regarded emulators such as [[higan]] or kevtris's work on the various FPGA-based consoles by Analogue. Just because an emulator claims to be "cycle accurate" or "100% compatible" does not mean that said emulator is flawless. This even includes situations in which all emulator accuracy tests (ie. [[PS1 Tests]]) are passed, as these tests cannot cover every single edge case, and some of these tests may even fail on real hardware, leading to even more confusion. Some things are nearly impossible to perfectly emulate, such as some of the illegal opcodes of the [[wikipedia:MOS_Technology_6502|6502]], where the results are completely unpredictable on hardware, and different hardware revisions have different results and different illegal opcodes. The closest one could get to writing a perfect emulator would be if someone were to exactly copy an original ASIC map or a decap onto an FPGA, and even then, that isn't always a magic bullet.
While any given emulator may not be perfect, that does not mean that the emulator is bad by any means. Writing an accurate emulator is extremely hard work, and while perfection may be nearly impossible at the moment, that doesn't mean that games can't be enjoyed. Work on archival via emulation has come a very long way since the emulators of the 1990s, and things are only getting better from here, with excellent emulators such as the previously mentioned [[higan]] and kevtris's [[FPGA ]] cores being available to use right now.
==Controversy==
==Console revisions==
Many consoles have different internal hardware revisions which degrade accuracy or change the consoles' behavior in another way, such as the SNES 1CHIP (various games have minor issues, such as a small mess of pixels at the top of the screen in games such as Super Ghouls 'n Ghosts or Demon's Crest), Genesis Model 3 (fixed a bug that some games such as Gargoyles used), various [[Commodore 64 emulators|Commodore 64]] revisions (fixed a useful bug that allowed for smooth horizontal scrolling), or PS2 SCPH-750XX (less compatibility with some PS2 games and PS1 games). These specific consoles are not generally emulated in their respective emulators, and those emulator developers tend to focus only on one revision. An exception to this is [[VICE]], which tries to emulate as many different revisions of the Commodore 64 as possible and as accurately as possible.
==Further reading==
