hard disk activity

[VSmirk]

I'm working primarily on Windows XP, but my solution needs to be cross
platform.

The problem is that I need more than the fact that a file has been
modified.  I need to know what has been modified in that file.

I am needing to synchronize the file on a remote folder, and my current
solution, which simply copies the file if a date comparison or a
content comparison, becomes a bit unmanageable for very large files.
Some of the files I'm working with are hundreds of MB in size, or
larger.

So I need to skip copying a hundred MB file that has had only a few
bytes changed and instead identify which few bytes have changed and
where those changes are.  I was thinking having a module that worked
below the file system level, at the device level, might be a place to
look for a solution.