Registers & Shift Registers: Definition, Function & Examples



A register is basically a an array or a group of flip-flops used for storing binary information. As we know that the flip-flop is the basic block of storage, one flip-flop can store one bit of information. For storing n-bit in register, it will require ‘n’ number of flip-flops. Registers are mainly used for storing and shifting information.

Registers finds its application in many other digital devices like serial adder , microprocessors , multipliers , dividers etc.

SHIFT REGISTER –  These register capable of shifting binary information either to the right or to the left is called shift register. The binary information within the register is shifted after each succeeding clock pulse.


Shift registers are classified into the following types based on the how the data is stored or shifted.

classification of shift registers

1. Serial-In Serial-Out (SISO)  This type of shift register accepts data serially i.e, one bit at a time. For entering the n-bit information in the register, n flip-flops will be required and ‘n’ number of clock pulses. And for retrieving the data (or shifting the data out from the register) stored in the register, again ‘n’ number of clock pulses will be required because data is shifting serially i.e, one bit at a time (clock pulse).

2. Serial-In Parallel-Out (PISO) – In this type of flip-flop, data is entered serially into register but the output from all the flip flop are taken out in parallel (all bit at a time). Therefore for entering the n- bit data, ‘n’ clock pulse will be required. But for retrieving the data (or shifting the data out from the register) all bits will be available simultaneously. But shifting the data out from register can only be done when the data is completely stored i.e, each bit should appear on its respective output line.

3. Parallel-In Serial-Out (PISO) –  As the name suggests, in this type of register the bits are added/entered simultaneously into their respective flip-flop. And the shifting the data out from the register is done serially i.e, on bit by bit basis.

4. Parallel-In Parallel-Out (PIPO) – In this type of register, the data is entered into the register simultaneously to their respective flip-flop and the respective bits will be generated at the output because of the parallel output. Since there is not serial shifting of data, so there is no interconnection between the successive flip-flop only clock is applied simultaneously to each flip-flop.

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