I have just run a full system scan.
The statistics at the end showed that Avast had tested 73.1 GB of data . . . . . but when I right-click on my hard-disk and look at it’s properties - it shows only 65.2 GB of it as being used !
How is this possible ? Where is the extra 7.9 GB of data that Avast thinks it has tested ?
I am using Windows XP and have only the one disk and it has only the one partition.
Thank you in advance.
David
Avast is probably counting the data in compressed files/folders in the total.
You’ll probably find that number of files checked is (possibly considerably) greater than number of files on the drive, for the same reason
When scanning files, avast! decompresses compressed files (i.e. zip archives) to check its contents. Since avast! decompresses a compressed file, the size of files scanned increases. 
You can’t compare used disk size whith total file size(s).
They are two different things.