What are shift registers? 

Shift registers refer to digital circuits where a cascade of flip-flops is used to connect the output of one flip-flop to the input of the next. A shared single clock signal between the flip-flops allows the stored data to shift from one place to another and this creates a cycle of data. Just as the first flip-flop is connected to the next, the last flip-flop is connected back to the first one, ensuring that the data cycle goes on for long periods. 

Types of shift registers

Shift registers can be categorised into four types, depending on the type of inputs they have. Typically, a shift register can have both parallel and serial outputs and inputs, configured in alternating types. As such, they can be categorised as:

• Serial-in serial-out shift registers (SISO)
• Serial-in parallel-out shift registers (SIPO)
• Parallel-in serial-out shift registers (PISO)
• Parallel-in parallel-out shift registers (PIPO)

Applications

Shift registers are used widely in digital electronic devices. Most commonly, they are used as memory elements in computers. For instance, they are typically used for:

• Data transfer 
• Data storage
• Data manipulation 
• Time delays
• Converting data