Simulator or Emulator? What is the difference?

Question

While I understand what simulation and emulation mean in general, I almost always get confused about them. Assume that I create a piece of software that mimics existing hardware/software, what should I call it? A simulator or an emulator?

Could anyone explain the difference in terms of programming?

Bonus: What is the difference in English between these two terms? (Sorry, I am not a native speaker :))

Answer 1

An emulator is a model of a system which will accept any valid input that that the emulated system would accept, and produce the same output or result. So your software is an emulator, only if it reproduces the behavior of the emulated system precisely.

Answer 2

The definitions of the words describe the difference the best. A google search gives the following definitions of simulate and emulate:

simulate imitate the appearance or character of.

emulate match or surpass (a person or achievement), typically by imitation.

A simulation imitates a system. An emulation simulates a system so well that it could replace it or may even surpass it.

In computing, an emulation would be a drop in replacement for the system it is emulating. Often times it will even outperform the system it is imitating. For example, game console emulators usually make improvements such as greater hardware compatibility, better performance, and improved audio/video quality.

Simulations, on the other hand, are limited by them being models. They are a best attempt to mimic a system, but not replacements for it. There are hardware emulators because hardware can be imitated and it would be hard to tell the difference. There is no Farming Emulator because there is no emulation that could replace actual farming. We can only simulate a model of farming to gain insight on how to farm better.

Answer 3

It's a difference in focus. Emulators¹ focus on recreating the behavior of a system, with no regard for how the system functions internally. Simulators² focus on modeling the components of a system. You use an emulator when you care mostly about what a system does, and a simulator when you care about how it does it.

As for their general English meanings, emulation is "the endeavor to equal or to excel another in qualities or actions", while simulation is "to model, replicate, duplicate the behavior, appearance or properties of". Not much difference. Emulation comes from æmulus, "striving, rivaling," and is related to "imitate" and "image," which suggests a surface-lever resemblance. "Simulation" comes from similis "like", as does the word "similar," which perhaps suggests a deeper congruence.

References:

1. Wikipedia: Emulator
2. Wikipedia: Computer Simulation
3. Wiktionary: emulation
4. Wiktionary: simulation
5. Etymology Online: emulation
6. Etymology Online: simulation

Answer 4

Simple Explanation.

If you want to convert your PC (running Windows) into Mac, you can do either of these:

(1) You can simply install a Mac theme on your Windows. So, your PC feels more like Mac, but you can't actually run any Mac programs. (SIMULATION)

(or)

(2) You can program your PC to run like Mac (I'm not sure if this is possible :P ). Now you can even run Mac programs successfully and expect the same output as on Mac. (EMULATION)

In the first case, you can experience Mac, but you can't expect the same output as on Mac.
In the second case, you can expect the same output as on Mac, but still the fact remains that it is only a PC.

Answer 5

In more or less normal parlance: If your software can do everything the mimicked system can do, it's an emulator. If it only approximates the results of a system (IT or otherwise), it's a simulator.

Answer 6

Some years ago I came up with a very short adage that, I believe, captures the essence of the difference quite nicely:

A simulator is an emulator on a mission.

By that I mean that you use an emulator when you can't use the real thing, and you use a simulator when you can't use the real thing and you want to find something out about it.