With four SR flip flops it can store upto 4 bits of data. Serial data is applied to S input of the first flip flop.
When serial data is transferred into the register, each new bit is clocked into first flip flop at the positive edge of each clock pulse. The bit that was stored by first flip flop is transferred to second flip flop and so on.
The shifting out of stored data 0101 serially from the register requires four clock pulses, which is represented as in the following truth table.
