TELETYPE MACHINES
Developed for telegraph 'hard copy' communication over the telephone network, a teletype machine was suited to adoption by the rapidly expanding computer market, with its demand for hardware and technology to run it. A ready-made printer and keyboard communication device, it was capable of being attached to the systems by the addition of data link hardware to handle the already established protocol. For this reason teletypes were used both in the computer room to operate the system, and by remote users to communicate with the system, to submit and retrieve information.
A Teletype was a common 'console', used by the operator. They were also used for remote printers connected to the computer by telephone wires via modems. Typically a KSR35 (Keyboard Send and Receive) using a series of characters on pins arranged in a square block. The block was moved to align it in front of a hammer used to strike the appropriate pin and transfer the ink from the ribbon to the paper.
Another common teletype, the ASR33 (Automatic Send and Receive) used a cylindrical block with characters etched on it to align vertically and horizontally clockwise or counter-clockwise, the appropriate character for printing. The operator, or other user, in each case could use the keyboard to input basic commands or data to the computer.
Another console communication device was a modified IBM Selectric or Remington SR-101 electric typewriter. They used a 'golf ball' to type in a similar way to the ASR33. With the addition of changeable 'balls' for a different font set.
These machines were better suited to computer interface as they were much faster than conventional type machines.
VIDEO TERMINALS
Consoles next moved into the 'modern' era when a CRT (Cathode Ray Tube) display was added. At first this was in addition to the to the typewriter device, as a console record was kept on paper to analyse what had happened at various stages of operation (so we know who to blame!).
Consoles have since become data terminals, with keyboard and screen, then mini computers incorporating maintenance and diagnostic capabilities, as well as console function. PCs, at first monochrome, then color, emulating a 'green screen' terminal, then using colors for different purposes, are standard today, as are LCD monitors.
Console records are still maintained on files, either in the PC on hard drive or on the mainframe, depending on the system. (you still can't get away with anything!) Some systems use a control console for each operation, system, network, printers etc. Others incorporate all functions in one control, with auxiliary stations in the print room, network console, etc.
NETWORKS
Networks, originally supported by modems at speeds of 110 baud gradually improved in speed along with modem technology to 9600. Connection methods were either RS232 standard, or some proprietary modified version of it, used by system manufactures to ensure customers used their terminals and printers.
The next stage was the adoption of Ethernet, or other contemporary protocols. Ethernet also increased from 10 to 100 to gigabit transmission rates. Terminals and printers at remote points improved from a basic dot matrix printer to which a monochrome terminal was added.
Currently remote users are using PCs or 'thin clients' (basically a pc with no hard drive, using the network server to download programs) with a laser printer dedicated or shared with a workgroup. A network of several hundred PCs and printers can be managed from a central 'network control', or at any point on the network.
Tony is an experienced computer engineer. He is currently webmaster and contributor to http://www.what-why-wisdom.com A set of diagrams accompanying these articles may be seen at http://www.what-why-wisdom.com/history-of-the-computer-0.html RSS feed also available - use http://www.what-why-wisdom.com/Educational.xml |
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