A common misconception is that everything you do on the internet is all processed over the internet and that its responsiveness depends entirely on the website and its servers. This is not the case. When a student clicks Start Lab in LabSim, the browser requests the necessary files to run the lab from cdn.testout.com. These files are downloaded and then temporarily stored and run by your computer. Once the loading bar disappears, the LabSim simulator uses very little internet and the responsibility to run the simulation falls upon your CPU, RAM, and browser. Depending on how fast your computer can process the information, your experience can vary greatly in terms of loading times, responsiveness, and overall time needed to complete the lab. The single greatest factor in lab speed and responsiveness is the CPU.
Not all CPUs are created equally. Depending on the quality and efficiency of your CPU, your computer might process the actions you take in the lab quickly, slowly, or it could get overwhelmed and become unresponsive.
The graph below shows the number of seconds it takes to complete an average lab based on the benchmark score of the CPU as found on www.cpubenchmark.net. 
The same person doing the same lab on the computer with the best CPU took only 146 seconds, while it took 1.85 times as long, 270 seconds, on the computer with the worst CPU. That is all after the lab is done with its initial loading, using the same internet, the same browser, and the same operating system. The CPU you have makes a HUGE difference in the experience you have while working in our labs.
We use a CPU benchmark score as a measurement that corresponds with the speed in which a lab can be completed. We have found that the clock speed (represented by GHz) advertised by CPUs may not accurately measure how it will perform with our product, but a third-party website called www.cpubenchmark.net has run thousands of CPUs through their own benchmark testing and assigned average scores to these CPUs. These benchmark scores correlate more precisely to the results that we have documented than any other measurement we have come across. We recommend anything as fast or faster than the AMD A12-9720P with its score of 3532. See full recommended technical specifications here.
Processors that do not meet the recommended speed may still work, but slowness may be a common occurrence.
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Recommended CPU Benchmark score ≥ 3500
See https://www.cpubenchmark.net/mid_range_cpus.html for a list of comparable processors.
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What does this mean for you? If you are struggling with slowness and unresponsiveness in LabSim, find out the name of your CPU and search for it on www.cpubenchmark.net. If the average score of your CPU is below 3500, then you may want to experiment on a computer with a CPU that meets or exceeds this recommended score.
If you find that your CPU is adequate, but you are still experiencing unreasonable levels of slowness, unresponsiveness, or freezing, try the troubleshooting ideas found in this linked article.