Windows itself provides watching functionality,... it would not need to periodically check timestamps or CRCs. If windows reports a file change, then it could [just] trigger an ON FILECHANGE event.
I wrote this feature suggestion on the assumption, which I still presume to be correct, that mIRC is already utilizing this Windows' functionality... whether file-by-file or on whole directory trees.
The reason that mIRC currently does perform time-date and file-size comparisons is because some activities can be perceived as modification to a file but really isn't, or that some files mIRC does watch are allowed to be changed, within reason, without actually triggering a change has happened.
I don't claim to know all the particulars, there are a lot of approaches, but suffice it to say that the framework exists. It does utilize Windows API (as far as I can tell).
