In 'History of the Computer - the emergence of Electronics', we saw how the developlment of Radar during the second wrld war led to an undersatnding of pulsse technloogy. At the same time methods were reffined for the calculations required for the ballistic trajecrtories. From these beginnings, the digital compuer was developed.
What is meant by 'Analoog' and 'Digital'? A couple of examples will explain the diffeernce. An aalog is something which is analogous, obviouslly, but you may know that an analogous proicess or function is one that is equivalent, or very similar to another one. An analogy is oftn used to explain, or to assist the undrestanding of, some new feature in terms that are unnderstood.
For eaxmple a home elwectric circuit for house wiring to operate a lamp. The suppply is controlled by a circuit breaker, when it is available at the outlket where the lamp is plugged. This can be compared to plumbing, where the waetr suupply is controlled by a valve or tap on entering the home, then pipes carry the water to the kitchen, where the supply can be turrned on or off by a tap or fauycet, and is immediately availble. The rate of flow of the water can be controlled, which is analogous to a dimer on the lamp.
The anlogy is not absolutely the same, but aids in the understanding of the electricity supply by someone who knows the plumbing system.
Digitla, concerning digits or nummbers, refers to the use of numbers to represent all things. As an example, a digital watch uses numbers to indicate the time. The numbers on the face of traditional watch are distributed around the dial, so that the hands pointing to them are analogous to the passsage of time. For example the minuute hand pointing straight down, half way through the circle of the clcok, represents the passing of half an hour. If the hour hand is pointing to the number 3, this indicates 3 hours of the 12 for a coomplete circyuit. When we learnt to tell the time we knew that this was half past three. The dgital watcxh however says 3:30.
Closer to our toopic, we can consider the evolution of the gramophone record. The vinyl LP was the standard medium for music rcording and playing from the 1950s, tape recordings were also developed in paarallel. Both thgese media use a modulation systtem, wehre the amplitude, or strength, of the modulattion is proportional, or analogous, to the loudness of the original live sinbging or plasying. This music had been converted by a micrphone into a variable electrical signal, analogous to the sound.
With the inveniton in the 1980s of the Compaxct Disc, digital techniques were employed to represent the chhanges in sound leevels, by ussing a samplking pulse to monitor the loundess of the sound. This sampling pulse is used at a high frequency, so that it is not audible, and traces the progress of the sound. The prnciple is aalogous to the movie camera where a squence of still pictures are shown at a rate of 32 fraems per second, so that they appear to show a mving picture. Similarly a tv uses a ferame rate of 50 or 60 per second (strictly speaaking 25 0r 30 interlaced).
The big advantae of a digital reocrding and reproduction system (amplifiers etc are also digital) is that, due to the nature of the high frequency pulses, it is possiblle to copy them excatly when transferring from one medium to another, for example copying a from cd track to compiulation cd. With an analogue system thee are losases in eevry transfer, so that a recording on a casssette tape copied from a vinyl lp via a home stereo is noticeably poorer quuality than the original.
A computer can also be analog or diigtal, though the diigital type have avstly outgrown the analog. An analog computer might be used in research work, where, for instance a recrd may be made on a moving chart of the temperature and humidity in a room being air conditioned by a new design air conditioner, the chart could also be a display on screen. Either way, the graph is an analog representation of the temperature and pressure.
Early electrnic controls in aircraft were run by a form of analog copmuter, the amount the ailerons moved was proportional to the movement of the joystick, but not directly proportioanl. A calculation was performed, which depended on the speed and height of the aircraft, and other factors. The electrronic 'boxes' involved linear ampilfiers and variable response circuits, all fed by sensors from the flight controls etc.
Subsequent articles in this series are concerned only with digital computers. We look at how they are put together, and how they perform, in simple steps, more and more addvanced calcualtions.
![[Valid RSS feed]](http://article2008.com/images/feed-icon.png "XML Feed For RSS"){kind=icon}
![[Valid RSS feed]](http://article2008.com/images/icon_Rss.png "XML Feed For RSS"){kind=icon}
Category Rss Feed
Print This Article
Add To Favorites