IO Hardware – Computers work on many types of devices. General types include storage devices e.g. disks, transmitters network cards, modems and human interface devices e.g. display, keyboard mouse. Other devices are more specialized. A device that communicates with a computer system by sending signals via a cable or even through the air. The device communicates with the machine by a connection point called a port for example, a serial port. If one or more devices use a common set of lines, the connection is called a bus. In other words, a bus is a set of wires and a rigidly defined protocol that specifies a set of messages which can be sent on the wires.
In case of when device A1 has a cable that plugs into device B, and device B has a cable that plugs into a device C, and device C plugs into a port on the computer, this organization is called a daisy chain. It generally operates as a bus.
A controller is basically a collection of electronics that can operate a bus, port, or a device. A serial-port controller is can be an example of a modest device-controller. This is only chip in the computer that controls the signals on the lines of a serial port. The SCSI bus controller is often applied as a distinct circuit board a host adapter which plugs into the computer. It holds a processor, microcode and some private memory to enable it to process the SCSI protocol messages. Some of devices have their own built-in controllers.
A computer system comprises with many types of I/O devices and their individual controllers
- Network Card
- Graphics Adapter
- Disk Controller
- DVD-ROM Controller
- Serial Port
- Sound Card
An I/O port normally involves four registers, called the control, status, data-in, and data-out registers.
|This register usually contains status bits that might read by host. These bits specify whether a byte is available to be read from the data in register or also indicate device error.|
|This register can be written by the host to alter the mode of the device. For example, a definite bit in the control register of a serial port chooses b/w full-duplex and half-duplex communication, another enables parity checking, a 3rd bit sets the word size to 7 or 8 bits, and other bits select one of the speeds sustained by the serial port.|
|This register is read by the host to acquire input.|
|This register is written by the host to send output data..|