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