Can someone explain me why AV’s like NOD32, AVIRA and KAV are so much lighter on resources than Avast! If they can establish this why can’t Avast! ? Take in consideration that I am a layman so please no to technical 
I’m sorry I don’t believe this to be correct in all cases as for many there is no direct comparison as they don’t have the same functionality.
I have also seen in these forums reports that having switched from KAV that their system was quicker with avast.
You also don’t provide any resource figures to compare against, you also don’t say what you consider to be resource use. Nor what functions are in use for these AVs to even attempt any comparison.
avast! is generally light on the conventional view of resources which seems to be RAM and CPU%.
david I am a layman concerning computers but … I can read ! I read several boards such as wilderssecurity etc… people with far more knowledge than me state on such MB’s that for instance NOD32 uses far less memory than Avast! … are they lying ? I don’t think so… I’m not judging I am only asking … :o
Lying? No. But they are usually wrong.
You know, you honestly cannot tell how much memory does an antivirus use unless you are its developer (and even in that case, you can speak only for your own product, so you can’t really compare with others). Checking the usual programs (Task Manager, Process Monitor) gives you some numbers - but they are usually misleading. Unless you know in detail how the program is implemented (what memory is shared between the modules, etc.), you can’t say that a program is using less memory (or other resources) than another one.
The only thing you can tell is your subjective impression about your system responsiveness (with the antivirus installed, as compared to the previous state) - but that’s something that may significantly differ accros systems (i.e. what’s fast on one computer may be slow on another, and vice versa). So, my advice is: try for yourself and stay with the product that suits you the most.
In the interests of research I just removed avast from my system and installed NOD32 (as a 30 day free trial).
Nice program.
Memory - the obvious stuff - two entries using about 30Mb (VMsize).
No noticeable affect on the usability of my system.
Restored my system back to running with avast.
Memory - the obvious stuff - 4 entries using about 41Mb (VMsize)
No noticeable affect on the usability of my system.
The memory size difference is a nit on my system (2Gb).
Given free versus annual fee and that avast has kept my systems virus free for several years (ie the entire time I have used it) the choice for me is an easy one.