All input and output devices like the keyboard, the printer and the mouse are connected to the system unit through ports. These ports are actually the inlets and outlets of the microprocessor. The microprocessor communicates with the outside world through them. These ports can be either serial or parallel. To transfer a byte through a serial port, eight bits are queued and sent bit by bit. However, in a parallel port, all the eight bits are transferred simultaneously.

If all PC components were made by the same manufacturer, there would be no problems in connecting the input and output devices to the system unit. But this is not always the case, and each manufacturer follows a different standard for transferring data. Thus, you may not be able to connect a brand X monitor to a brand W computer. The solution to this problem lies in standardizing the way data is transferred.

Serial Port Standard

The industry standard for serial transfer of data is the RS-232C port. This standard defines the various parameters for data transfer, one of them being the speed of transfer. A mouse, for example, uses RS-232C port for communicating with the CPU.

Parallel Port Standard

An industry acknowledged parallel port standard is the Centronics printer interface developed by the makers of the Centronics printers. Printers normally use this standard.