MadSci Network: Computer Science

Re: what is digital, how does it work.

Date: Thu Dec 7 10:21:34 2000
Posted By: Yiannis Mavroukakis, Grad student, MSc Advanced Software Engineering, University of Westminster
Area of science: Computer Science
ID: 976073644.Cs

I assume that by asking, what is digital, you mean what is the difference
between a digital and an analogue design or signal.
The easiest comparison that comes to mind, is one of a telephone line
carrying data.
Imagine that the data in the analogue case, is carried as high pitched
sounds (modem "shrieks") which are translated at the modem into data. The
"shrieks" are the way the data has to travel down a line designed for
analogue operations. If you examine a waveform for an analog transmission,
you will observe that it has lots of irregular peaks and valleys. The
problem that this carries is this: When the analogue signal is carried
over long distances it tends to degrade, and introduce errors to the
signal. Because of the nature of the waveform, those errors cannot be
easily identified and rectified.
Now, the digital signal is quite different. Instead of irregular peaks and
valleys in the waveform, you have a nice clear signal that looks something
like this:

         _______      ______            ______
        |       |    |      |          |      |
        |       |    |      |          |      |
        |       |    |      |          |      |
________|       |____|      |__________|      |_________

That looks much nicer doesnt it? Not only does it look nice, it is also
much easier to detect and correct errors in the stream. The reason behind
this is in the logic of the digital stream itself. Data is transmitted as
differences in the voltage applied to the line, commonly +5 volts for a
binary 1 and 0 volts for a binary 0. Whatever device is at the other end,
makes sense of the digital data, in the way it was programmed to do. The
digital signal is also much easier to "boost" for transmission over long
distances, again because of the waveform type.

I hope this is what you were looking for.


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