Learning Resources

I/O Ports and Peripheral Interfaces

I/O ports -

I/O stands for Input and Output. The most common device for input is the keyboard. When you type, you are putting information into the computer, which is known as input. The most common device for output is the monitor. After the information has made its way through the computer, it is sent out to the monitor for us to see. This is known as output. On the back of computers are several I/O, (or Input/Output), ports. Above, on the very top are two PS/2 ports, normally used for mouse and keyboard connections. Below that are the USB, (or Universal Serial Bus), ports.

In computing, input/output or I/O is the communication between an information processing system (such as a computer) and the outside world, possibly a human or another information processing system. Inputs are the signals or data received by the system, and outputs are the signals or data sent from it. The term can also be used as part of an action; to "perform I/O" is to perform an input or output operation. I/O devices are used by a person (or other system) to communicate with a computer. For instance, a keyboard or a mouse may be an input device for a computer, while monitors and printers are considered output devices for a computer. Devices for communication between computers, such as modems and network cards, typically serve for both input and output.

An I/O interface is required whenever the I/O device is driven by the processor. The interface must have necessary logic to interpret the device address generated by the processor. Handshaking should be implemented by the interface using appropriate commands (like BUSY, READY, and WAIT), and the processor can communicate with an I/O device through the interface. If different data formats are being exchanged, the interface must be able to convert serial data to parallel form and vice-versa. There must be provision for generating interrupts and the corresponding type numbers for further processing by the processor if required.

As shown below -

Peripheral Interfaces

With the steadily declining costs and size of integrated circuits, it is now possible to include support for many peripherals on the motherboard. By combining many functions on one PCB, the physical size and total cost of the system may be reduced; highly integrated motherboards are thus especially popular in small form factor and budget computers.

For example, the ECS RS485M-M, a typical modern budget motherboard for computers based on AMD processors, has on-board support for a very large range of peripherals:

  • Disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0/1 support)
  • integrated graphics controller supporting 2D and 3D graphics, with VGA and TV output
  • integrated sound card supporting 8-channel (7.1) audio and S/PDIF output
  • Fast Ethernet network controller for 10/100 Mbit networking
  • USB 2.0 controller supporting up to 12 USB ports
  • IrDA controller for infrared data communication (e.g. with an IrDA-enabled cellular phone or printer)
  • Temperature, voltage, and fan-speed sensors that allow software to monitor the health of computer components

As shown in the schematic -