Why does an empty loop use so much processor time?

Question

If I have an empty while loop in my code such as:

while(true);

It will drive the processor usage up to about 25%. However if I do the followin

Answer 1

Sleep() is not really doing anything during the period that the thread is sleeping. It hands its time over to other processes to use. A loop on the other hand is continuously checking to see if the condition is true or false.