One problem in electronics is drift, where the circuits lose the bit boundaries in a long stream of pure 1's or pure 0's. The disk drive is spinning quite rapidly, but there are often minor variations in speed which make it impossible for the electronics to stay perfectly in sync for more than about 8 bits. Thus, a string of ASCII NULLs (00000000) or all 1's would confuse the disk drive and its attached controller.

Fig. 17.3.1 illustrates how two computers which are communicating over a modem, or two devices communicating over a bus, can misinterpret the bit stream if their clocks are not perfectly in synchronization. Since the receiver's idea of a bit slice is "wider" than the sender's, the receiver will sample parts of the incoming signal at later and later times, eventually skipping an entire bit.