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Difference between Emulator and Simulator

By Sourojit Das, Community Contributor -

Sometimes, software testers can be heard talking about Emulators and Simulators in the same breath. It almost seems as if these two terms are synonymous. From a purely semantic point of view, a thesaurus might consider these two terms to be akin to each other. However, any diligent software test leader needs to be cognizant of the differences between the two in order to make the most of each type of test tool. 

But before diving into the differences between Emulators and Simulators, it is important to figure out why they are used in the first place and what they actually are.

An Introduction To Mobile Testing Device Solutions

Mobile App testing requires the execution of test suites to make check the functionality, performance, usability, etc of the application meet the technical and business requirements expected from it. With over 6.2 billion smartphone users as of 2021, it’s massive that the mobile app testing sector has acquired great significance in the testing world. 

With the expected revenue from mobile apps reaching $935 billion by 2023, companies must adopt quality mobile device testing solutions that enable them to conduct comprehensive testing in a cost-effective and time-efficient manner with a good ROI (Return on Investment).

It is famously said that one of the biggest misconceptions in testing is to consider mobile apps as software for smaller screens. The app is ideally designed for devices that are structurally and logically different from the workstations that they are programmed on, and browser window resizing is often not a complete reflection of compatibility. 

Such devices need to be tested early and within mobile environments for context and compatibility. The main reason software test leaders focus on mobile testing solutions is to guarantee that the consistent behavior of websites or mobile apps on different mobile devices for a seamless user experience. These mobile devices differ by hardware configuration, OS, and screen resolutions, and often what seems to render well in one instance may look distorted in others, which is why cross platform testing is important.

It is pivotal to choose the correct test method to maximize the efficiency of the mobile app tests. Moreover, it is also essential to Test on the right mobile devices for more accurate results that can help identify the bottlenecks and rectify them. Hence understanding Testing Devices is a must to leverage them for delivering quality mobile applications.

In the subsequent sections, let’s check out the different types of mobile devices for testing.

Real and Virtual Testing Devices

There are mainly two types of devices on which mobile testing is conducted:

  • Real Devices
  • Virtual Devices – Emulators vs Simulators

Real Devices refers to the various mobile handset models available in the open market to run the website on and are used to test the functionality and behavioral patterns of the application. These are the exact actual devices that end-users will use.

Testing teams generally prefer to buy a few handsets with iOS/Android and test their applications on them. And, though the results generated from these tests are as close to real-world results as a team would get, the high costs and overheads like updating your device sets from time to time can prove prohibitive. One should definitely read about the Build vs Buy Framework.

This turned out to be a big enough challenge for companies to seek refuge in virtual testing devices such as Simulators and Emulators. These devices came to the forefront while testing cross browser compatibility for the software.

A Virtual Testing Device (including both emulators and simulators) is a piece of software that provides a virtual simulation of the most important features of an actual smartphone or mobile device. It mimics the nature of the said device to help testers run the software application and obtain an idea of how it would run on a real device for an end user.

What are Emulators?

Emulators mimic the target device’s hardware and software on a workstation. Android Emulator by Android Developer Studio is a popular example. 

Read More: What are Android Emulators?

Computers, including those on mobile devices, work on an ISA (Instruction Set Architecture). These are machine language commands that the processor understands, and different processor families like Intel, AMD, ARM, etc., have their own ISAs. These emulators mimic the device’s processor and then translate the ISA commands from the workstation to those the device understands. This is done through binary translation.

The emulator can provide a virtual device instance with near-native capabilities to adjust the devices’ physical sensors, battery state, geolocation, etc. However, emulators cannot create real user conditions for testing such as network simulation, push notification, etc. as offered by real devices.

Test on Real Devices 

Limitations of Emulators

However, these emulators are not without their limitations. These near-native capabilities come with a significant performance overhead, mostly due to binary translation. And though  hardware-assisted virtualization can speed this up, there are still issues with:

  • Matching the ISA’s of the computer being used to perform the test and the mobile device as most commercially available mobile devices run on ARM’s architecture and computers use Intel x86. 
  • Also, it is tricky to set up the multiple hypervisor components which are required to set up hardware-assisted virtualization

When to use Emulators

Emulators are optimal when the test focuses on how the software interacts with the underlying hardware or any combination of hardware and software. Some common scenarios for their use are:

  1. To figure out whether a firmware update will cause issues for the application
  2. Evaluating the performance of an application on different CPU types, and memory allocations. 

Emulators can be unreliable when testing android apps. Given their limitations, they cannot create a perfect simulation of the real-world conditions expected and may lead to inconclusive or even inaccurate results, which can be tedious.

You don’t have to know coding to make use of interactive cross browser testing tools. Browserstack Live, for instance, is also used by marketers and web designers who are quickly testing landing pages/new designs for cross-browser rendering and responsiveness.

What are Simulators?

Simulators allow the execution of programs that were not made for the workstation’s original OS. Testers commonly use these in mobile app testing to run their code, especially in the initial stages of development.

There are no ‘Android simulators’ since it is relatively easy to simply emulate Android devices using tools like Quick Emulator (QEMU).

Limitations of Simulators

iOS simulators work by sitting on top of the native OS, mimicking iOS, and executing your app within itself. This is viewable in either an iPhone or an iPad-like window and can be interacted with using a keyboard or mouse.

While this is faster than the Android emulator as there is machine-language translation involved. This simulator cannot mimic battery states or cellular interrupts as there is no hardware-mimic capability.

Also, the iOS simulator cannot be hosted on platforms other than macOS as it needs Apple’s native Cocoa API, and it is too troublesome to port this massive framework library to other platforms.

Where to use Simulators

Simulators are optimal for testing scenarios focused on ensuring that an application performs as expected during its interactions with external applications or environments.

For example, while testing an application’s ability to send data to another, a simulated environment is usually sufficient as the intrinsic hardware config is unlikely to play a significant role.

Test on Real Device Cloud

Differences between Emulator and Simulator

Here is a detailed tabular comparison between Emulator vs Simulator.

It mimics the entirety of the software, underlying hardware, and the OS of an actual device It mimics the Internal behaviour of the mobile device
Manufacturers or OEMs typically provide emulators for their platforms.Manufacturers or other organisations provide simulators.
Programs are written in Machine-level assembly language.Programs are written in High-level language.
Emulators are reliable and more suitable for debuggingSimulators, on the other hand, are less reliable and not so suitable for debugging
Binary translation makes them slower due to latencySimulators are faster as there is no Binary Translation

On a closing note

Both Simulators and Emulators offer several advantages when used diligently and can deliver optimized results for their respective scenarios. 

In general, virtual test devices offer a comprehensive debugging facility and are better placed to be used in the earlier part of the software development cycle to ensure a quick turnaround.

However, due to a lack of accuracy stemming from an inherent gap in their capabilities as compared to Real Devices, Sanity Testing, and User Acceptance Testing can be better done with real devices. Parts of Regression testing could still be done using virtual devices after a point, it might result in compromised results.

For some scenarios, it is impossible to gauge how the software works without placing it in a real-world context. No emulator or simulator can replicate real user conditions and therefore should not be considered a viable option for testing.

BrowserStack offers 3000+ real browsers and devices for both manual interactive testing and automated Selenium testing. They are hosted on the cloud, which allows them to be accessible from anywhere at any time. One simply has to sign up, log in, and start testing for free.

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