The Growth of Telegraphy

The essential techniques of sending data along wires has a history of 150 years, and some of the common terminology of modern data transmission goes right back to the first experiments.The earliest form of telegraphy, itself the earliest form of electrical message sending, used the remote actuation of electrical relays to leave marks on a strip of paper. The letters of the alphabet were defined by the patterns of 'mark' and 'space'. The terms have come through to the present, to signify binary conditions of '1' and '0' respectively. The first reliable machine for sending letters and figures by this method dates from 1840; the direct successor of that machine, using remarkably unchanged electromechanical technology and a 5-bit alphabetic code, is still widely used today, as the telex/teleprinter/teletype. The mark and space have been replaced by holes punched in paper-tape: larger holes for mark, smaller ones for space. Synchronisation between sending and receiving stations is carried out by beginning each letter with a 'start' bit (a space) and concluding it with a 'stop' bit (mark). The 'idle' state of a circuit is thus 'mark'. In effect, therefore, each letter requires the transmission of 7 bits: . * * . . . * (letter A: . = space; * = mark) of which the first . is the start bit, the last * is the stop bit and * * . .. is the code for A. This is the principle means for sending text messages around th world, and the way in which news reports are distributed globally. And, until third-world countries are rich enough to afford more advanced devices, the technology will survive. Early computer communications When, 110 years after the first such machines came on line, the need arose to address computers remotely, telegraphy was the obvious way to do so. No one expected computers in the early 1950s to give instant results; jobs were assembled in batches, often fed in by means of paper-tape (another borrowing from telex, still in use) and then run. The instant calculation and collation of data was then considered quite miraculous. So the first use of data communications was almost exclusively to ensure that the machine was fed with up-to-date information, not for the machine to send the results out to those who might want it; they could wait for the 'print-out' in due course, borne to them with considerable solemnity by the computer experts. Typical communications speeds were 50 or 75 baud. (The baud is the measure of speed of data transmission: specifically, it refers to the number of signal level changes per second and is thus not thesame as bits-per-second.)
 These early computers were, of course, in today's jargon, single-user/single-task; programs were fed by direct machine coding. Gradually, over the next 15 years, computers spawned multi-user capabilities by means of time-sharing techniques, and their human interface became more 'user-friendly'.With these facilities grew the demand for remote access to computers, and modern data communications began.Even at the very end of the 1960s when I had my own very first encounter with a computer, the links with telegraphy were still obvious. As a result of happenstance, I was in a Government-run research facility to the south-west of London, and the program I was to use was located on a computer just to the north of Central London; I was sat down in front of a battered teletype--capitals and figures only, and requiring not inconsiderable physical force from my smallish fingers to actuate the keys of my choice. As it was a teletype outputting on to a paper roll, mistakes could not as readily be erased as on a VDU, and since the sole form of error reporting consisted of a solitary ?, the episode was more frustrating than thrilling. VDUs and good keyboards were then far too expensive for'ordinary' use.