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Mastering Comput-ing, W.Buchanan, Palgrave

Isn't that interesting?

From 60 to a Billion in 30 Years

14 July 2001 WORK IN PROGRESS!

he 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

This 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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