Also consisting of arrays of bi-stable elements, the shift registers described in Module 5.7 are temporary storage devices (memories) for multi-bit digital data. The data can be stored in the register either one bit at a time (serial input) or as one or more bytes at a time (parallel input).
The register can then output the data in either serial or parallel form. Shift registers are vital to receiving or transmitting data in digital communications systems. They can also be used in digital arithmetic for operations such as multiplication and division.
A simple arithmetic and logic unit (ALU) is described in Module 5.8 and combines many of the combinational and sequential logic circuits described in modules 4 and 5 to demonstrate how a very complex application is built by combining a number of much simpler digital sub circuits.