I have some quiestions about how AntiVirus Software works.

Most of AVs likes to be registred as Service, but why?
//I know that it is the best startup way with windows

I want to know which AV can be installed without registrering of services and work as standard scanner without realtime protection.


I want to run more then one AV on my PC.

I have right now Avast and DrWeb installed on my conputer and thay works good. But Which more AV is possible to use like this?