Serial versus Parallel I/O

Parallel	Serial
1.      In parallel I/O, a byte of data is transferred at a time thus necessitating an 8-bit buffer or latch.	1.      In serial data must be transferred a bit at a time. Parallel I/O is thus reasonably straightforward as witnessed by the simple single-byte parallel I/O.
2.      Parallel I/O is quite simple.	2.      Since the data present on a microprocessor bus exists primarily in parallel from (it is ‘byte wide’), serial I/O is little more complex. Serial input requires a means of conversion of serial input data to parallel data in a form, which can be presented to the bus. Serial output, on the other hand, requites a means of conversion of the parallel data present on the bus into serial output data.
3.      Used generally for devices around the CPU, where large chunks of data are to be exchanged. Peripheral devices like printer use this mode of operation.   When transmitting digital information over long distances, however, providing 8 wires or 8 simultaneous communication channel may be too expensive for the application.	3.      Serial data transmission is used generally in long distance communication, since only a pair of wire is required to transmit or receive data.        Only serial data transmission is useful for internet because preexisting network of telephone can be used and it will also reduce the cost of multiple wire as required in parallel data communication.
4.      Theoretically, Parallel data transmission is 8 times faster than serial data transmission. Thus it is generally used in devices where speed matters.	4.      Slower than parallel