The input/output processor or I/O processor is a processor separate from the CPU designed to handle only input/output processes for a device or the computer.
The I/O processor is capable of performing actions without interruption or intervention from the CPU. The CPU only needs to initiate the I/O processor by telling it what activity to perform. Once the necessary actions are performed, the I/O processor then provides the results to the CPU. Doing these actions allow the I/O processor to act as a bus to the CPU, carrying out activities by directly interacting with memory and other devices in the computer. A more advanced I/O processor may also have memory built into it, allowing it to perform actions and activities more quickly.
For example, without an I/O processor, a computer would require the CPU to perform all actions and activities, reducing overall computer performance. However, a computer with an I/O processor would allow the CPU to send some activities to the I/O processor. While the I/O processor is performing the necessary actions for those activities, the CPU is free to carry out other activities, making the computer more efficient and increase performance.