Hardware, software or a combination of the two that enables a computer to act like another computer and run applications written for that computer. In the past, it was often a hardware add-on that actually contained an instruction execution module for the emulated computer. Today, "emulator" more often refers to software, which provides a translation layer from the emulated computer to the computer it is running in. The emulator may translate machine language, calls to the operating system or both. Contrast with simulator. See x86 emulator, terminal emulation, Wine, 3270 emulator, disk emulator, FX 32, ROM emulator, ICE, Mac emulator and Virtual PC for Mac.