Hello,
you are mistaken; if you install Avast, several shields are active: File Shield (scans files that are being opened), Web Shield (scans web browsing traffic), Mail Shield (scans incoming mail). These scan for threats all the time, and are the most important part of Antivirus; scanning your disk time to time is good, but without shields, antivirus is nearly useless. We update virus definitions every few minutes, and scan stuff that is being actively accessed, so there is a maximal chance of stopping threats.
Additionally, it is useless to look at anything else than Private memory (memory which is owned by the process and needs to be kept in memory or swap file); the remaining is usually binaries and memory mapped files backed by real files, which means it can be paged out of memory at any time when memory becomes scarce. As you can see, the only processes that consume significant memory is daemon (unpacked virus definitions of scan engine) and proxy (state of all http connections). In general, size of binaries is not really relevant for real application memory footprint.
Avast uses multiple processes to be more reliable (if one part crashes, rest continues running), so the process count is high, but they do not do much in general, sometimes very little.
Kind regards,
Ondrej Kolacek
