I used the C standard I/O `fseek' to create a file which had 50% holes in it. BUT I don't know how to confirm this on Windows. With the same source code compiled on Linux, and then to use `du' and `ls -l' commands I can tell there are holes in the created file (`du' shows almost half size of `ls -l'). On windows, Unfortunately, right click the file, select properties, "size" and "size on disk" are nearly same. So I'm not sure about the holes really exist. Anyone can help? How to check?