Well my question here is an Honest one - I am not here to compare different products.

Here’s a quote from another AV maunual:
“*** saves system resources
and reduces computing work
to a minimum. The file caching
system developed in order to
save time “memorises” which
files have been examined and are
therefore clean. A rescan only
occurs if the files have been
changed in any way”

This is done via some sort of checksum system (like MD5) - so if the file is altered/infected/updated whatever it is scanned.

Either way I thought this was common?