We’ve seen in the History of the Computer series how machine code is used to run a computer so that it can use the 1s and 0s to interpret the intentions of a program. But what about a code for human communication with the computer? We may differently write and read on different media, such as paper tapes, magnetic tapes, disks or teleprinters, but we need ways to convert English (or another language) into a form compatible with these supports.
You may remember old Western movies where the James gang fired on the telegraph operator so he could not call the Marshall for help. Or the movies on the crash of 29 Wall Street where the tycoon reads the bad news on the ticker and jumps quickly from the window of the 32nd floor. These two examples are early examples of using a code on a medium. In this case, the Morse code on the telegraph and an analog code produced from a keyboard located at the point of transmission are also sent by telegraph. The teletypewriter ribbon, so called because of the noise caused by the printing mechanism, carried the stock code, as used in the current stock market, as well as an estimate.
A poster code used for the paper tape, the baudot code, named after the French inventor Baudot, was a five-bit code, engraved on the tape, giving a pattern 1 and 0 to compose the 26 letters of the alphabet . The tape was an inch wide and came on large spools. A pinion hole was drilled in the tape so that it could be moved into the drive.
As we know from our analysis of the binary codes, 5 bits will give us a total of 31 characters (1 + 2 + 4 + 8 + 16) plus zero. Since 26 characters are used for the English alphabet, the other characters are used for carriage return, line feed, and so on. They are needed to use the typewriter used to print the information. Another character, Bel, was ringing on the typewriter to alert the operator.
Later, a Shift character was embedded, similar to the Shift key of a typewriter, so the following characters indicate numbers. Another offset code would be letters. This Baudot code was used on teletypes to transmit data from one place to another. This was then accomplished by first tapping the tape and then transmitting it to a “high speed” player. These speeds were gradually increased as the technology improved, and were generally expressed as “baud rate”, roughly equivalent to the number of bits per second, also named after Baudot . Most of the problems are due to punching errors and synchronization of the transmitter and receiver.
