From 60 to a Billion in 30 Years
July 2001 WORK IN PROGRESS!
communications industry has moved from transmitting a single character every second,
to transmission many billions of characters every second. The great breakthrough
has to communicate faster than someone could type. One of the most basic communications
rate is actually based on the speed of a typist. For this a good typist will type
at around 75 words per minute. If we assume that there are five characters on
average in every word (with an extra character for a space). Thus the typist will
type, on average, 450 characters per minute. This will give 7.5 characters ever
second. Thus, as each character is represented, in ASCII, with 8 bits. The maximum
transfer rate will be:
Transfer rate = 7.5 (characters per second) x 8 (bits
per character) = 60 bps
was the basic bit rate that a communications link would have to support if it
were to receive the speed of a fast typist. When a faster rate was required, the
basic rate was doubled to 120bps (although the standard rate was typically set
at 110bps). The speed then to a jump to 300bps, and multiples of this followed
with 1200bps, 2400bps, 9600bps, 19,200bps (19bkps), 38,400bps (37kbps), 57,600bps
(56kbps), 115,200bps (112kbps), and so on. Most serial communications ports for
computers and modems support many of these rates.
From the starting rate
of 60 bps, the rates have increased over the years, as more people have used communications
links, and backbone data traffic can have a capacity of tens of billions of bits
per second (a 166,666,667 fold increase). For example, this chapter contains over
84,000 characters. With a 60bps transfer rate it would take over 3 hours to transmit
it, while at 10 billion bits per second it would be transmitted in less than 100
millionth of a second (assuming a transfer rate of 10,000,000,000 bits per second
for 672,000 bits). The basic bit rate of transmission will increase over the years
as the demand for data communi-cations increases, and the number of applications
for it increases.
Chapter 7, Mastering Computing, W.Buchanan, Palgrave.
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