Emulator vs. Simulator: What’s the Difference?

While emulators and simulators may initially seem identical, there exists important differences between the two. But what are they? And why should you care?

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Image: Sofy x Simakova Mariiam, Shutterstock

Mobile device emulators and simulators are commonly encountered tools in contemporary mobile testing and, in fact, development in general. They operate in a virtual environment, making them cheaper and more convenient than setting up a real device lab.

While we’ve covered the topic of emulators versus real devices on the Sofy Blog in the past, but we’ve encountered some confusion about simulators and emulators. So, let’s take a look at how simulators and emulators differ and overlap.

Similar but different

In practical terms, for some applications and some engineers, mobile device emulators and mobile device simulators might as well be the same thing.

The dictionary definitions of the two terms make differentiation even harder. The Merriam-Webster dictionary definition of emulate is just to imitate. To simulate is to give or assume the appearance or effect of often with the intent to deceive; imitate.

That said, having the same word in their dictionary definitions does not mean the two technical systems work in the same way, nor do they have the same use cases. They are not the same thing.

We’ll break down the similarities and differences between emulators and simulators and in which circumstances a programmer might use one over the other.

What an emulator and a simulator have in common

Both emulators and simulators are types of virtual machines that model an environment to test applications. They can also monitor the virtual machine itself for changes in the test, problems that arise, and more.

Because emulators and simulators have similar use cases and appear at the same point in the development pipeline, engineers often use these terms interchangeably, but each has its own unique use cases, strengths, and weaknesses that are important to remember when choosing one over the other.

A brief guide to emulators

Emulators provide engineers with a less hypothetical option between the two. They act as a bridge between real hardware and the pure software environment of a simulator.

An emulator aims to imitate everything about a production environment, as well as the actual device that will run the software. Like all virtual machines, it essentially runs a computer inside another computer. However, an emulator also imitates the behavior of the hardware and operating system to attempt to replicate a realistic test of the user experience.

Technical aspects

Emulators are often written in an assembly language so engineers can conceivably replicate every single detail of the deployment device’s performance, including:

  • Changes in battery performance
  • Updates to the operating system
  • Changes in clock speed
  • Temperature

The computer that runs the emulator must imitate an entire piece of hardware. While this setup requires substantial resources, an emulator can therefore potentially imitate any device. This approach can potentially accelerate the testing timetable. With high-quality emulators, devs can test their programs on many workstations without having to procure and update the real machine.

Use cases

Emulators are most useful when a team:

  1. Does not have access to a real device lab
  2. Works with a wide variety of devices
  3. When engineers need to prepare for real system use

The first point here is especially important. Real-life applications and all their variations are no match for an emulator, which remove any hypotheticals about how a real system behaves.

Ultimately, emulators provide the same results as a real object, provided the emulator is programmed well enough. They provide a scalable method of testing that is easily accessible; engineers can select a testing device from a large library of virtual machines and choose the one they need at that point.

Weaknesses

Emulators have their weaknesses. For example, they require far more system resources to run since they perform binary translation, which leads to latency. Thus, they aren’t suited for tests that require low latency or in instances where latency can add up and take up too much time.

They must also run in real-time or near real-time, so they aren’t useful for many non-software applications. Modeling geological time changes, for example, might need to run at 1,000 years every second to provide useful data. An emulator can’t do that, but a simulator can.

In a more relevant development case, engineers might need to measure how a system degrades over time. An emulator would need to run for the same amount of time as the real version would, which could take months or years.

For that situation, a simulator makes for a better fit.

A brief guide to simulators

A simulator is still a virtual machine, but unlike an emulator, it imitates the software behavior and only that behavior. Simulators are more useful for situations that require analysis, like academic studies and hypotheticals, than they are for real-world analyses.

Technical aspects

Unlike emulators, simulators do not interact with virtualized hardware at all. Tests that use simulators are simply not concerned with hardware factors.

As a software-only environment that bypasses the hardware to run software in isolation, engineers can construct simulators with higher-level programming languages. They also perform no binary translation, so they can operate with less latency.

Use cases

The decreased latency is a valuable benefit for tight development deadlines or large programs that require huge resources to operate.

In general, simulators work best for situations that involve software testing with little to no interaction with the underlying hardware. If the production environment is any of the following, then a simulator should provide sufficient testing information for software (and it will work only with the software):

  • System-agnostic
  • Operating out of the cloud
  • High performance enough to make system performance a non-factor

For example, simulators can imitate large CRM applications that can run on any enterprise system that is more than capable of handling its data. Simple cross-device changes like resolution or display aspect ratio fit well in simulations, too.

Though the latter examples are hardware changes, their effects can be analyzed with a few changes to the software display, so there is no need to emulate an entire system for something as simple as display output.

Weaknesses

Simulators, by their nature, cannot test the ways that software interacts with hardware. They work fast and give engineers a flexible method for tests but are primarily hypothetical. Compared to emulators, they are not well-suited to real-world, practical use cases.

This is because they are designed to imitate the behavior of a system rather than calculate all its processes in detail.

The difference between an emulator and simulator

To put it simply, a simulator tests how an application should run, while an emulator tests how an application will run on the selected hardware that it is ultimately meant to. To a simulator, the mechanics don’t matter at all. If the mechanics do matter, then an emulator is the right choice.

Emulators vs. simulators in mobile testing: Considerations

When deciding on an emulator or simulator for application testing, the first step is to identify the kind of testing you need. Do your engineers need to know how the application will interact with the hardware and operating system they expect it to use, or can they afford to analyze it in a pure-software environment?

Is the hardware that the system will run on relevant to its performance? If so, an emulator is the right choice. Does the test measure a situation that extends over a long period of time? If so, then a simulator will help more.

It’s entirely possible to use several of both in a single development cycle or neither at all. Thanks to modern cloud testing, you can test on multiple real hardware devices without ever leaving your main workstation, directly on your browser, with a larger library of virtual and real devices than your team could afford to collect.

Sofy makes for a good example: With Sofy, you and your team can access real devices via the cloud, eliminating any emulator guesswork and ensuring your app behaves as you’d like on actual devices.

Disclaimer: The views and opinions expressed above are those of the contributor and do not necessarily represent or reflect the official beliefs or positions of Sofy.

 

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