| In 'History of the Computer - the emergence of | | | | modulation system, where the amplitude, or |
| Electronics', we saw how the development of | | | | strength, of the modulation is proportional, or |
| Radar during the second world war led to an | | | | analogous, to the loudness of the original live |
| understanding of pulse technology. At the same | | | | singing or playing. This music had been converted |
| time methods were refined for the calculations | | | | by a microphone into an variable electrical signal, |
| required for the ballistic trajectories. From these | | | | analogous to the sound. |
| beginnings, the digital computer was developed. | | | | With the invention in the 1980s of the Compact |
| What is meant by 'Analog' and 'Digital'? A couple | | | | Disc, digital techniques were employed to |
| of examples will explain the difference. An analog | | | | represent the changes in sound levels, by using a |
| is something which is analogous, obviously, but | | | | sampling pulse to monitor the loudness of the |
| you may know that an analogous process or | | | | sound. This sampling pulse is used at a high |
| function is one that is equivalent, or very similar | | | | frequency, so that it is not audible, and traces the |
| to another one. An analogy is often used to | | | | progress of the sound. The principle is analogous |
| explain, or to assist the understanding of, some | | | | to the movie camera where a sequence of still |
| new feature in terms that are understood. | | | | pictures are shown at a rate of 32 frames per |
| For example a home electric circuit for house | | | | second, so that they appear to show a moving |
| wiring to operate a lamp. The supply is controlled | | | | picture. Similarly a TV uses a frame rate of 50 or |
| by a circuit breaker, when it is available at the | | | | 60 per second (strictly speaking 25 0r 30 |
| outlet where the lamp is plugged. This can be | | | | interlaced). |
| compared to plumbing, where the water supply is | | | | The big advantage of a digital recording and |
| controlled by a valve or tap on entering the | | | | reproduction system (amplifiers etc are also |
| home, then pipes carry the water to the kitchen, | | | | digital) is that, due to the nature of the high |
| where the supply can be turned on or off by a | | | | frequency pulses, it is possible to copy them |
| tap or faucet, and is immediately available. The | | | | exactly when transferring from one medium to |
| rate of flow of the water can be controlled, which | | | | another, for example copying a from CD track to |
| is analogous to a dimmer on the lamp. | | | | compilation cd. With an analogue system there are |
| The analogy is not absolutely the same, but aids | | | | losses in every transfer, so that a recording on a |
| in the understanding of the electricity supply by | | | | cassette tape copied from a vinyl lp via a home |
| someone who knows the plumbing system. | | | | stereo is noticeably poorer quality than the original. |
| Digital, concerning digits or numbers, refers to the | | | | A computer can also be analog or digital, though |
| use of numbers to represent all things. As an | | | | the digital type have vastly outgrown the analog. |
| example, a digital watch uses numbers to indicate | | | | An analog computer might be used in research |
| the time. The numbers on the face of traditional | | | | work, where, for instance a record may be made |
| watch are distributed around the dial, so that the | | | | on a moving chart of the temperature and |
| hands pointing to them are analogous to the | | | | humidity in a room being air conditioned by a new |
| passage of time. For example the minute hand | | | | design air conditioner, the chart could also be a |
| pointing straight down, half way through the circle | | | | display on screen. Either way, the graph is an |
| of the clock, represents the passing of half an | | | | analog representation of the temperature and |
| hour. If the hour hand is pointing to the number 3, | | | | pressure. |
| this indicates 3 hours of the 12 for a complete | | | | Early electronic controls in aircraft were run by a |
| circuit. When we learnt to tell the time we knew | | | | form of analog computer, the amount the ailerons |
| that this was half past three. The digital watch | | | | moved was proportional to the movement of the |
| however says 3:30. | | | | joystick, but not directly proportional. A calculation |
| Closer to our topic, we can consider the evolution | | | | was performed, which depended on the speed |
| of the gramophone record. The vinyl LP was the | | | | and height of the aircraft, and other factors. The |
| standard medium for music recording and playing | | | | electronic 'boxes' involved linear amplifiers and |
| from the 1950s, tape recordings were also | | | | variable response circuits, all fed by sensors from |
| developed in parallel. Both these media use a | | | | the flight controls etc. |