What is d difference between serial and parallel data transfer?

Answer 1

As an example of serial data transfer using the shift register approach, a set of four shifts triggered by clock pulses places the contents of the X-register into the Y-register. Since four clock cycles are needed, it is much slower than parallel transfer, but is simpler and cheaper.

The illustration below shows the parallel transfer of 8 bits of data from the X Register to the Y Register upon application of an enabling transfer pulse. Clearly, parallel data transfer is faster than serial data transfer, but serial transfer has the advantages of requiring less hardware. These registers are made up of D flip-flops, which can serve as memory locations. The information in the X Register is intact after the transfer to the Y Register, so this process shows a possible scenario for accessing digital information stored in memory.