Is System drive included in All harddisks (precluding the need to have both option included in a scan), or are they different?
Is System drive included in All harddisksYes. Note the [b]ALL[/b] ;)
The system drive is the most important drive.
Active infections will always involve the system drive.
On other drives there can be Terra-bytes of data that someone doesn’t want to be checked each time.
Right, but if I want all drives to be scanned in my custom scan, I don’t need to also add the “System drive” option, as that’s already included in “all drives”.
I don’t know why you would bother with a custom scan, just use the Full System Scan.
Personally - With a resident on-access antivirus like avast, the need for frequent on-demand scans is much depreciated. For the most part the on-demand scan is going to be scanning files that would be otherwise be dormant or inert. If they were active files then the on-access file system shield would be scanning them before being created, modified, opened or executed.
I used to have avast set to do a scheduled weekly Quick scan, set at a time and day that I know the computer will be on. But I have ceased this practice for some time now, based in the above.