Q. What is Input-output processors?

let's briefly summarize the development in area of input/output functions. These can be briefed as below:

1. CPU directly controls a peripheral device.

2. Addition of I/O controller or I/O interface: CPU employs programmed I/O with no interrupts. CPU was separated from details of external I/O interfaces.

3. Contained use of I/O controllers however with interrupts: CPU need not spend time waiting for an I/O operation to be executed, increasing efficiency.

4. Direct access of I/O interface to memory through DMA: CPU involvement decreased to at beginning and at end of DMA operation.

5. CPU directs I/O processors to execute an I/O program in memory. I/O processor fetches as well as executes these instructions with no CPU intervention. This permits CPU to specify a series of I/O activities and to be interrupted only when complete sequence has been performed. With this architecture a large set of I/O devices can be managed with minimum CPU involvement.

With last two steps (4 and 5) a main change takes place with introduction of concept of an I/O interface capable of executing a program. For steps 5 the I/O interface is frequently referred to as an I/O processor and I/O channel.