1857 AD |
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| In 1837, the American inventor Samuel Finley Breese Morse developed the first American electric telegraph, which was based on simple patterns of "dots" and "dashes" called Morse Code being transmitted over a single wire. | The telegraph quickly proliferated thanks to the relative simplicity of Morse's system. However, a problem soon arose in that operators could only transmit around ten words a minute, which meant that they couldn't keep up with the public's seemingly insatiable desire to send messages to each other. This was a classic example of a communications bottleneck. | |
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| Thus, in 1857, only twenty years after the invention of the telegraph, Sir Charles Wheatstone (the inventor of the accordion) introduced the first application of paper tapes as a medium for the preparation, storage, and transmission of data. | ||
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| Sir Charles' paper tape used two rows of holes to represent Morse's dots and dashes. Outgoing messages could be prepared off-line on paper tape and transmitted later. |
Wheatstone's perforated paper tape |
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| By 1858, a Morse paper tape transmitter could operate at 100 words a minute. Unsuspectingly, Sir Charles had also provided the American public with a way to honor their heroes and generally have a jolly good time, because used paper tapes were to eventually become a key feature of so-called ticker-tape parades. | ||
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| In a similar manner to Sir Charles' telegraph tape, the designers of the early computers realized that they could record their data on a paper tape by punching rows of holes across the width of the tape. The pattern of the holes in each data row represented a single data value or character. The individual hole positions forming the data rows were referred to as "channels" or "tracks," and the number of different characters that could be represented by each row depended on the number of channels forming the rows. | The original computer tapes had five channels, so each data row could represent one of thirty-two different characters. However, as users began to demand more complex character sets, including the ability to use both uppercase characters ('A', 'B', 'C', ...) and their lowercase equivalents ('a', 'b', 'c', ...), the number of channels rapidly increased, first to six and later to eight. | |
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This
illustration represents one of the more
popular IBM standards -- a one-inch wide tape supporting eight channels (numbered from 0
to 7) with 0.1 inches between the punched holes. The first paper tape readers accessed the data by means of springy wires (one per channel), which could make electrical connections to conducting plates under the tape wherever a hole was present. These readers were relatively slow and could only operate at around fifty characters per second. |
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| Later models used opto-electronic techniques, in which a light source was placed on one side of the tape and optical cells located on the other side were used to detect the light and thereby recognize the presence or absence of any holes. | ||
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| In the original slower-speed readers, the small sprocket holes running along the length of the tape between channels 2 and 3 were engaged by a toothed wheel to advance the tape. The higher-speed opto-electronic models used rubber rollers to drive the tape, but the sprocket holes remained, because light passing through them could be detected and used to generate synchronization pulses. | On the off-chance that you were wondering, the reason the sprocket holes were located off-center between channels 2 and 3 (as opposed to being centered between channels 3 and 4) was to enable the operator to know which side of the tape was which. Of course, it was still necessary to be able to differentiate between the two ends of the tape, so the operators used scissors to shape the front-end into a triangular point, thereby indicating that this was the end to be stuck into the tape reader. |
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| These notes are abstracted from the book Bebop BYTES Back (An Unconventional Guide to Computers) Copyright Information |
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