An emulator duplicates (provides an emulation of) the functions of one system using a different system, so that the second system behaves like (and appears to be) the first system. This focus on exact reproduction of external behavior is in contrast to some other forms of computer simulation, which can concern an abstract model of the system being simulated.

Emulators in computer science

A hardware emulator is an emulator which takes the form of a hardware device. Examples includes the DOS-compatible card installed in some old-world Macintoshes like Centris 610 or Performa 630 that allowed them to run PC programs and FPGA-based hardware emulators.

In a theoretical sense, the Church-Turing thesis implies that any operating environment can be emulated within any other. However, in practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware, possibly triggering time interrupts to alter performance.

Emulation in preservation

Emulation is a strategy in digital preservation to combat obsolescence. Emulation focuses on recreating the original computer environment and can be time-consuming and difficult, but valuable because of its ability to maintain a closer connection to the authenticity of the digital object.

Emulation addresses the original hardware and software environment of the digital object, and recreates it on a current machine. The emulator allows the user to have access to any kind of application or operating system on a current platform, while the software thinks it is in its original environment. Jeffery Rothenberg, an early proponent of emulation as a digital preservation strategy states, “the ideal approach would provide a single extensible, long-term solution that can be designed once and for all and applied uniformly, automatically, and in synchrony (for example, at every refresh cycle) to all types of documents and media”. He further states that this should not only apply to out of date systems, but also be upwardly mobile to future unknown systems. Practically speaking, when a certain application is released in a new version, rather than address compatibility issues and migration for every digital object created in the previous version of that application, we could create one emulator for the application, allowing access to all of said digital objects.

Benefits

• Emulators maintain the original look, feel, and behavior of the digital object, which is just as important as the digital data itself.
• Despite the original cost of developing an emulator, it may prove to be the more cost efficient solution over time.
• Reduces labor hours, because rather than continuing an ongoing task of continual data migration for every digital object, once the library of past and present operating systems and application software is established in an emulator, these same technologies are used for every document using those platforms.
• Many emulators have already been developed and released under GNU General Public License though the open source environment, allowing for wide scale collaboration.