5 Examples of computers
5.1 The personal computer
Over the following screens you will look at three different examples of computers: a PC, which is obviously a computer, and a set of electronic kitchen scales and a digital camera, which are not so obviously computers. You will find that all three of these examples match with the functional block diagram of a computer given in Figure 3 in Section 2.3, although the tasks they have to perform mean that the individual components which perform the functions of the blocks within the diagram are quite different.
In Activities 2 and 3 you looked at how the components of the laptop in Figure 2 could be related to the functional block diagram in Figure 3. Figure 6, which is a functional block diagram for the laptop and shows the data flow between the components of the laptop in Figure 2, should remind you of the outcome. Notice that in this diagram I have put in specific input and output devices and specific items of secondary memory instead of the generic items of Figure 3. In other words, Figure 3 is a generic diagram for any computer; Figure 6 is its specific form for the laptop of Figure 2.
Other PCs may have some additional input devices such as a web cam, plus some additional output devices such as a printer.
The PC is a general-purpose computer. It can run different software programs at the user's request, and hence can be used for a variety of different applications. Typical examples are word processing, sending and receiving email, playing games, browsing the web, and sound and image recording and playback.
The following quote from the book A Shortcut through Time, The Path to Quantum Computing by George Johnson shows that even those long familiar with the concepts of how PCs work can still find them fascinating. (A register is a part of a processor and the term ‘disk drive’ is often used to describe either a floppy disk or hard disk.)
With a modern PC we blithely double-click an icon on the desktop summoning a flow of data from the disk drive – the pattern of bits that configures thousands of little switches to act as a word processor or a web browser or an MP3 player – temporary little structures, virtual machines. They are allowed to exist only as long as they are needed. Then they are wiped away and replaced with other structures, all built from 1s and 0s.
It is hard to believe sometimes how well this works. You can call up a movie trailer in a window and drag the image around the desktop, causing millions of bits to pour through the computer's hidden registers. It is overwhelming to try and imagine the precise coordination going on behind the screen. Ultimately though it all comes down to shuffling 1 s and 0s, flipping little switches on and off.
(George Johnson, A Shortcut through Time, The Path to Quantum Computing)
Earlier you looked at how data can be represented by bits – two bits can represent four items, three bits eight items, four bits sixteen items, etc. This is fine if, for example, you want to represent a clearly defined set of data such as the letters of the alphabet and numbers. But how are the images of the ‘movie trailer’ in the above quote represented in your computer? How can you turn your image into items that can be represented by bits? As you will see from the next two examples, electronic kitchen scales and a digital camera, this issue of data representation exists in all computers.