Explain the Parallel In - Parallel Out Shift Registers?

For "parallel in - parallel out" shift registers all data bits show on the parallel outputs immediately following the simultaneous entry of the data bits.

The following circuit is a "four-bit parallel in - parallel out shift register" constructed through D flip-flops.

The Q's are the parallel outputs and The D's are the parallel inputs. Once the register is clocked then all the data at the D inputs appear at the corresponding Q outputs simultaneously.