 <p>Signed variables use one bit to flag whether they are positive or negative. Unsigned variables don't have this bit, so they can store larger numbers in the same space, but only nonnegative numbers, e.g. 0 and higher.</p> <p>For more: <a href="http://www.rwc.uc.edu/koehler/comath/13.html" rel="nofollow noreferrer">Unsigned and Signed Integers</a></p>