Serial port and parallel port

December 2016

Serial ports are generally built into the mother board, which is why the connectors behind the casing and connected to the mother board by a wire cable can be used to connect an exterior element. Serial connectors generally have 9 or 25 pins and take the following form (DB9 and DB25 connectors respectively):

DB9 connector


DB25 connector


A personal computer generally has between one and four serial ports.

Parallel port

Parallel data transmission involves sending data simultaneously on several channels (wires). The parallel ports on personal computers can be used to send 8 bits (one octet) simultaneously via 8 wires.

transmission on a parallel port


The first two-way parallel ports allowed for speeds of 2.4Mb/s. Enhanced parallel ports have been developed however to achieve higher speeds:

  • The EPP (Enhanced Parallel Port) achieves speeds of 8 to 16 Mbps
  • The ECP (Enhanced Capabilities Port), developed by Hewlett Packard and Microsoft. It has the same characteristics as the EPP with in addition a Plug and Play feature, allowing the computer to recognise the connected peripherals.



Parallel ports, like serial ports, are built into the mother board. DB25 connectors allow connection to an exterior element (e.g. a printer).

DB25 connector


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