input_output device

Input–output (I/O) devices vary substantially in their characteristics. One distinguishing factor among input devices (and also among output devices) is their data processing rate, defined as the average number of characters that can be processed by a device per second It has been indicated in the introduction part that there exists a big difference in the rate at which a processor can process information and those of input and output devices. One simple way to accommodate this speed difference is to have the input device simple way of communication between the processor and I/O devices, called I/O protocol, requires the availability of the input and output registers. In a typical computer system, there is a number of input registers,each belonging to a specific input device first arrangement, I/O devices are assigned articular addresses, isolated from the address space assigned to the memory. The execution of an input instruction
at an input device address will cause the character stored in the input register of that device to be transferred to a specific register in the CPU.This arrangement, called shared I/O,The second possible I/O arrangement is to deal with input and output registers as if they are regular memory locations. In this case, a read operation from the address
corresponding to the input register of an input device, for example, Read Device 6, is equivalent to performing an input operation from the input register in Device #6. Similarly, a write operation to the address corresponding to the output register of an output device