Single file exclusions are allowed (without any path fragment, whatsoever). Your example of pagefile.sys is special in a way that it needs not be excluded, see KB82021.
As for your other examples, the engine examines only the first 3 letters of the extension, that is, you need not specify any more letter: excluding A.sys will result in exclusion of A.sys1, or A.sys123456. See also Related information in KB58707.
Use in below format :
PageFile.sys or must they be specified as **\PageFile.sys.
A.sys1 A.sys2 and A.sys3 = A.sys*
Thanks Attila, I'm aware of the 3 char extension limit, my example is purely theory. I guess I'm wondering what overhead a long list of exclusions has.
Not sure if this will help, but here is the KB on Managing File Exclusions, and as ansarias points out the 'Double Asterisk' is common practise.
Certified McAfee Product Specialist - ePO
As far as I remember there is nothing to worry about performance until around 1000 single exclusions are specified (have read somewhere here or gotten as a reply to my post in the past).
•The ? wildcard is used to represent a single character in the exact position where it is placed in the path or file name.
•The * wildcard is used to represent partial filenames or extensions with one or more characters from the exact position where it is placed in the path \ file given.
•The ** wildcard is generally used for (partial) filenames or extensions with one or more characters from the exact position where it is placed in the path \ file given.
•System Environmental Variables such as %SystemRoot% can be used in exclusions. User Environmental Variables such as %UserProfile% cannot because the On‑Access scanner runs under the Windows Local System account.