- Note: This category is not intended to catalog every emulator in existence, only those emulators which stand out and which people wish to write about and support on StrategyWiki.
From the point of view of games, an emulator is a piece of software that makes it possible for a game or other program to run on a different platform than the the one for which it was written. The emulator aims to make the program behave in exactly the same way on the new platform as it would have on the original one. Two main types of emulator are relevant to games: processor emulators and operating system emulators.
A processor emulator aims to work round the fact that different processors, especially if they are of different generations, have different machine languages and therefore a program produced for one processor is unintelligible to another. The processor emulator reads the instructions that were produced for processor A and translates them into processor B's machine language "on the fly". It also has to do some translation in the other direction, for example by translating processor B's interrupts (event signals) and presenting them to the program in the format used by processor A.
The most prominent processor emulator among emulation fans is MAME, which allows you to play on your personal computer many programs that were written specifically for arcade machines. Besides arcade games, emulators have been written for a variety of home console systems, such as the NES, Super Nintendo, and Sega Genesis, and a great number of earlier home computer systems, such as the Atari 800, Commodore 64/128, and Sinclair ZX Spectrum.
An operating system emulator aims to work around the fact that that different operating systems have different APIs (application programming interfaces, i.e. conventions for requesting services from the operating system, such as allocating memory, drawing on the screen and detecting keyboard, mouse and joystick actions), incompatibilities that would otherwise be crippling even though the processor can handle the program's machine language. One of the best-known operating system emulators is DOSBox, which makes it possible to run most DOS games on Windows, Mac OS and Linux systems.
Both types of emulation use much more processor power and memory than the games would have required on their original platforms, but they perform well enough because modern computers are vastly more powerful than those for which the games were written.