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One of the best-known software errors occurred on 22 July 1962 when the Mariner I rocket had to be blown-up, after it followed an erratic path after it took off. It was caused by a single incorrect character in a FORTRAN statement for the motion equations.

In 1963, ANSI defined the 7-bit ASCII standard code for characters. At the same time IBM had developed the 8-bit EBCDIC code which allowed for up to 256 characters, rather than 128 characters for ASCII. It is thought that the 7-bit code was used for the standard as it was reckoned that eight holes in punched paper tape would weaken the tape. Thus the world has had to use the 7-bit ASCII standard, which is still popular in the days of global communications.
Key characters to remember are:
'A' 41h 0100 0001
'a' 61h 0110 0001
'0' 30h 0011 0000

LF 0Ah 0000 1010
CR 0Dh 0000 1101

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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