Sometimes there is a non-degenerate pre-period part before the period: 13/10 = 1.0100110011 = 1.0(1001) as a binary fraction, the "1.0" part being the pre-period and the "(1001)" part the period. The same goes for decimal fractions.
Sorry, I meant 13/10 = 1.0100110011..., that is, the "1001" part repeating forever - as opposed to just stopping at 10-th bit of the fraction.
