CFile is a general class for doing file I/O. There are various subclasses of CFile, such as CMemFile and CInternetFile, which get their data from somewhere other than a disk.
A CArchive object can wrap anything derived from CFile, including CMemFile etc. (which is probably what Tom was thinking of). It lets you do things like:
Code:
CFile file("file.txt");
CArchive ar(&file);
ar << "Hello, world");
MFC's CDocument class uses CArchive to load and save data. If you look at the CDocument implementation for a text editor application generated by Class Wizard, you will see that the document's Serialize() method just uses the CEditView to read and write to and from the archive.