What is WIO in Sar reports

When analysing sar data, one of the parameters that causes lots of confusion is the wio (or wait for IO) value.  It is counted in CPU reports as part of the CPU time, but is it really used CPU time?

If you look at the picture below you can see that even KSAR (http://sourceforge.net/projects/ksar/) makes it red in his graphs:

If you look closely, you can see that the red part is bigger at times when the blue and green parts are smaller.  This is a first indication that the red part is not literally a problem.

When a process has to wait for IO, it is shifted of the CPU.  If the CPU is able to wait (if it has some CPU time to spare), it will wait for the IO, so it can be handled immediately.  The time the CPU lets the process wait for IO, is the red part.

However, if the CPU has no time, and is more in use, it will shift the process to wait in a queue.  At that point, the CPU is able to serve other processes while the first process waits.

So, we can say that the WIO is significant, but it is not real "busy" time.