History of the Computer; Analog or Digital?

In 'History of the Computer - the emergence ofmodulation system, where the amplitude, or strength, of
Electronics', we saw how the development of Radarthe modulation is proportional, or analogous, to the
during the second world war led to an understandingloudness of the original live singing or playing. This
of pulse technology. At the same time methods weremusic had been converted by a microphone into an
refined for the calculations required for the ballisticvariable electrical signal, analogous to the sound.With
trajectories. From these beginnings, the digital computerthe 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. Anin sound levels, by using a sampling pulse to monitor
analog is something which is analogous, obviously, butthe loudness of the sound. This sampling pulse is used
you may know that an analogous process or functionat 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 theto the movie camera where a sequence of still
understanding of, some new feature in terms that arepictures are shown at a rate of 32 frames per
understood.For example a home electric circuit forsecond, so that they appear to show a moving picture.
house wiring to operate a lamp. The supply isSimilarly a tv uses a frame rate of 50 or 60 per
controlled by a circuit breaker, when it is available atsecond (strictly speaking 25 0r 30 interlaced).The big
the outlet where the lamp is plugged. This can beadvantage of a digital recording and reproduction
compared to plumbing, where the water supply issystem (amplifiers etc are also digital) is that, due to
controlled by a valve or tap on entering the home, thenthe nature of the high frequency pulses, it is possible to
pipes carry the water to the kitchen, where the supplycopy them exactly when transferring from one
can be turned on or off by a tap or faucet, and ismedium to another, for example copying a from cd
immediately available. The rate of flow of the watertrack to compilation cd. With an analogue system there
can be controlled, which is analogous to a dimmer onare losses in every transfer, so that a recording on a
the lamp.The analogy is not absolutely the same, butcassette tape copied from a vinyl lp via a home
aids in the understanding of the electricity supply bystereo 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 ofdigital type have vastly outgrown the analog. An
numbers to represent all things. As an example, aanalog computer might be used in research work,
digital watch uses numbers to indicate the time. Thewhere, for instance a record may be made on a
numbers on the face of traditional watch aremoving chart of the temperature and humidity in a
distributed around the dial, so that the hands pointing toroom being air conditioned by a new design air
them are analogous to the passage of time. Forconditioner, the chart could also be a display on screen.
example the minute hand pointing straight down, halfEither way, the graph is an analog representation of
way through the circle of the clock, represents thethe temperature and pressure.Early electronic controls
passing of half an hour. If the hour hand is pointing toin aircraft were run by a form of analog computer, the
the number 3, this indicates 3 hours of the 12 for aamount the ailerons moved was proportional to the
complete circuit. When we learnt to tell the time wemovement of the joystick, but not directly proportional.
knew that this was half past three. The digital watchA calculation was performed, which depended on the
however says 3:30.Closer to our topic, we canspeed and height of the aircraft, and other factors.
consider the evolution of the gramophone record. TheThe electronic 'boxes' involved linear amplifiers and
vinyl LP was the standard medium for music recordingvariable response circuits, all fed by sensors from the
and playing from the 1950s, tape recordings were alsoflight controls etc.Tony is an experienced computer
developed in parallel. Both these media use aengineer.