Why are some antivirus engines light as a feather and possess no impact on system performance while others bog down the system? What is it about these security products' programming that creates this variation?
It completely depends upon the antivirus configuration and how it is made. Some antivirus tool slows down computer system and takes most of the memory space; while some work silently in the background without disturbing any process of your system. Like Windows Defender, Immunet Plus Antivirus, Bitdefender, Avira, AVG etc. are some examples of light virus protection tool which does not affect computer’s speed or any of its process.
It just depends on their optimization and what they run in the background/actively. The ones that are as light as a feather are probably doing little more than looking for patterns in small sections of downloads. The heavier ones are probably going meticulously through every download or running auto-scans. Make sure that you don't have a scan running since that will slow it down significantly. Also, perhaps set their system priority lower so that it won't eat your processing power away if you are running some more powerful program.
