What are the different types of shift registers?

Shift registers are classified by input/output configuration: SISO (Serial-In Serial-Out) for data delay lines, SIPO (Serial-In Parallel-Out) for serial-to-parallel conversion, PISO (Parallel-In Serial-Out) for parallel-to-serial conversion, and PIPO (Parallel-In Parallel-Out) for temporary storage. Shift registers can shift left, right, or be bidirectional. Applications include data conversion, data storage, delay generation, and as building blocks for pseudo-random sequence generators.