title: Why is the CPU not needed to service I/O requests?
body: <p>I am learning about operating systems but there is a small concept I cannot grasp. Say a process 1 is running on the CPU and then it issues an I/O request to read from a disk. For efficiency, the CPU begins executing process 2 as this request is handled. That all makes sense but doesn't the I/O need to use the CPU?</p>
  
  <p><img src="https://i.stack.imgur.com/52in9.png" alt="enter image description here"></p>
  
  <p><strong>My Question:</strong> Why isn't the CPU needed to service process 1's request?</p>