What is the Difference between a Serial and Parallel Port

In computer, ports are mainly used for two purposes i.e. for:

      Device Control and       Communication

Parallel Port and serial port are both used for connecting external devices to the computer.

A Serial connection is a sequential one way connection over a wire while a Parallel connection is a way to speed up the connection by allowing the transfer of more data at the same time in the same direction and over multiple wires. In serial connection, there are two data lines:

      Transmission Line (a single wire takes information out) and       Receive Line (single wire will bring information in)

Some bits such as start bit, stop bit and parity bits to detect errors are used in serial ports while in parallel port, all 8 bits are sent to the port at a time and indication is sent in another line. There are some data lines, control and handshaking lines in parallel port.

Parallel ports are faster but are not used for long distance communication. This is because parallel ports needs a number of transmission lines. The reason, why the serial port results in slower transfer is that the packets are arranged in a queue first while in case of parallel ports; more bits are sent as the bits are not to be translated as in the case of serial ports.

The shape of the two ports is also different. Serial Port connection is like stringed beads, while parallel port connection can be complicated by a number of simultaneous transmissions of data. E.g. SATA hard drives have a serial interface.

Parallel programs are easy to program as compared to Serial ports. Parallel port uses a 25 pin connector (type DB-25) and is used to connect printers, computers and other devices that need higher bandwidths while a Serial port can be used for serial communication which transmits only 1 bit at a time. Examples of serial technology are USB and Fire-wire with IEEE 1284.

Parallel ports usually work on lower frequency to avoid any crosstalk. Parallel ports are usually purple in color while serial ports come in light green color. Most of the serial lines will be used for control functions and grounding functions while few parallel pins (usually 8 pins) are used for sending data.