How less hard disk space?

Users questions: My hard drive is 80G, but the computer, my c drive as 8.03G, D drive to 24.2G, E set to 24.2G, F set to 18G, a total of only 74.43G, how this is going on, and the rest how those space gone? little more than 5 G are normal?
Experts answer: addition to the above Said, ntfs partition too little space than fat32.
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