| At the heart of digital photography is the computer, yet | | | | the appropriate type for specific parts of the computer |
| when you open a computer you find mostly air and a | | | | - the key component being the central processor unit |
| board with a- few tiny items attached. The most | | | | (CPU). |
| remarkable fact about this assembly of items is that if | | | | One way to visualize the CPU is to imagine that a city |
| there is the slightest fault in any one of them, then the | | | | has a traffic system in which every junction is |
| computer will probably not work at all. This gives us an | | | | controlled by a set of lights, and that at each junction |
| insight into the way computers work: a strict hierarchy | | | | the lights can order a car to turn left, right, stop, and so |
| of control and instructions so interrelated that the | | | | on. When you load a program, such as an |
| failure of one exchange can bring the whole system | | | | image-manipulation application, into the CPU, you are |
| down. | | | | programming the way the traffic lights work. Now if |
| At the top of the hierarchy is you: by turning on the | | | | you speed up the vision, so that the cars are electrical |
| computer and entering commands via the mouse or | | | | pulses and the lights change hundreds of millions of |
| keyboard, you tell components in the computer what | | | | times a second, you are close to seeing how a CPU |
| to" do. Data goes into a controller, which turns it into | | | | works. |