Differences between settings you are talking about are:
- by default avast! Professional Edition scans only some archives. When you check “All archives” avast! will try to recognize all known archives a tries to scan their content.
- only files that can be infected are tested by default settings of avast! If you choose “all files” avast! will scan really all found files on your harddrive (or whatever you are scanning). So for example text files (.txt) or pictures (.jpg, .gif, .bmp, …) are also scanned for virus samples.
- avast! does not check whole files by default, it scans its begin and end as viruses mostly infects only these file parts. There is a settings “Test whole files” in task settings that you can enable and avast! will check whole files.
If you have checked mentioned check boxes avast! will need much more time to scan your harddrive. The reasons of it are:
- scanning of 50000 files will take much more time then scanning of 20000 files,
- expanding archives results into more files to be scanned,
- scanning some 16 KB from each file will take more time then scanning them whole