This excellent article by Gustavo Duarte explains what is going on when you are waiting for your computer to do something. If the language is a bit technical for you, a summary is:—
Consider your super-fast computer and compare that with finding information by hand. Getting data from the CPU cache memory is like picking up a paper from your desk—perhaps 3 seconds. Getting it from the second level cache is equivalent to a well indexed book near your desk—say 14 seconds. Getting it from main memory is a four minute stroll down the corridor to the stationary cupboard. Now, wait for it, fetching it from the hard drive is equivalent to sending Stanley to find Dr. Livingstone—One year and three months. If it’s on the internet then you may as well wait for NASA to launch the next Mars Probe and hope it comes back.