The minimum system requirements for PlayOn are listed here:

http://www.playon.tv/support/minreqs

The most important requirement is the processor. To make it easy to determine if a processor meets the requirements, you can check the PassMark score. To find your processor's PassMark score, it is easiest to search Google for PassMark <your processor's model>. You can also search the PassMark benchmark website:

CPU Benchmark Charts

A score of 500 or higher is required, but it is recommended that the processor score a 1,000 or higher. If you think you will want to watch two or more videos simultaneously or use the PC while streaming a video, a higher score will be required. Multiple the score by the number of video streams you will want to stream simultaneously.

Two streams will require a score of 2,000+

Three streams will require a score of 3,000+

It's a good idea to count using the PC as an additional video stream, so include that into your calculations. If you want to use the PC and stream two videos at once, then try to install the software on a PC with a PassMark score of 3,000+. This will allow you to stream two videos at high quality and use the PC without it feeling sluggish.

You can get by with a lower score by lowering the video performance setting inside PlayOn and PlayLater's settings managers.