What exactly do you understand by the term index file? Many of these terms are loosely used and mean different things to different people.
1) You could do an fseek to various locations in the file
2) It could be a file which is read into memory and then when a specified record is required, it looks up the index and seeks to that location.
3) Same as 2 but the index is stored in the form of a B-tree.
These are just three different interpretations of index file. If you could be more specific, then the MVPs won't assume the wrong things and give you something you aren't looking for.
