The concept of input output processor is an extension of the concept of DMA. The input output processor can execute specialized input output program re-sending in the memory without intervention of the CPU. Thus, CPU only needs to specify a sequence of input output activity to input output processor. The input output processor then executes the necessary input output instructions which are required for the task; and interrupts the CPU only after the entire sequence of input output activity as specified by CPU have been completed.
An advanced input output processor can have its own memory, enabling a large set of input output devices to be controlled without much involvement from the CPU. Thus, an input output processor has the additional ability to execute input output operations. Thus, input output processors are much more powerful than DMA which provides only a limited control of input output device.
For example, if an input output devices is busy then DMA will only interrupt the CPU and will inform the CPU again when the device is free while input output device and once it has found to be free go ahead with input output and when input output finishes, communicate it to the CPU. The input output processor is termed as channel in IMB machines.
In computer systems which have IOP's the CPU normally do not execute input output data transfer instructions. Input output instructions are stored in memory and are executed by IOP's. The IOP can be provided with the direct access to the memory and can control the system bus. An IOP can executes a sequence of data transfer instructions involving different memory regions and different devices intervention of the CPU.
An advanced input output processor can have its own memory, enabling a large set of input output devices to be controlled without much involvement from the CPU. Thus, an input output processor has the additional ability to execute input output operations. Thus, input output processors are much more powerful than DMA which provides only a limited control of input output device.
For example, if an input output devices is busy then DMA will only interrupt the CPU and will inform the CPU again when the device is free while input output device and once it has found to be free go ahead with input output and when input output finishes, communicate it to the CPU. The input output processor is termed as channel in IMB machines.
In computer systems which have IOP's the CPU normally do not execute input output data transfer instructions. Input output instructions are stored in memory and are executed by IOP's. The IOP can be provided with the direct access to the memory and can control the system bus. An IOP can executes a sequence of data transfer instructions involving different memory regions and different devices intervention of the CPU.
