I need help!

I am implementing file mappings, and I don't really understand what the Allocation Granularity is.

Firstly I don't want to view the full file. I only want to view the parts of the file I am interesting in. For instance there is a header, index, and body. Intially a process will be looking at the header, and index in order to determine whereabouts in the body to get the information I actually want from. The file is also going to be around 6Mb so copy Maps would seem to be very expensive (the view is copied into the processes memory location?)

Anyway I use SYSTEM_INFO to get the allocation granularity of the system, but I don't know how to transform this information into a file byte offset; specifically the high, and low order offsets required by the MapViewOfFile function

Help!

Yr