A Brief History of Computer Terminals

Compared to modern devices like the iPhone and iPad the very first computers seem very archaic indeed. They were large, often requiring huge custom built rooms to house them, they were delicate, needing large air conditioners and constant cooling to remain operational, and they were slow. The earliest systems could handle only a single job at a time and programs needed to be fed directly into the system through punch cards, magnetic or paper tape.

As computer systems evolved and became more capable efforts were made to make more effective use of the available computing power. Operating systems and technologies were developed that allowed multiple users to access the host system from a comfortable location both simultaneously and interactively. One of those technologies was the computer terminal.

Computer terminals were devices typically consisting of a cathode ray display tube and a keyboard that was used to interact with a host system. Early terminals were referred to as ‘Green Screens’ thanks to the very common monochrome phosphor display screens sported by the majority of terminal screens. Another common nickname was ‘Dumb Terminal’ in reference to the fact that all processing was handled by the host system and the actual terminals could do almost nothing for themselves. In fact, the host computer needed to constantly check the connection to the terminal to determine whether there had been any input from the user. This placed a large load on the main processing unit with much valuable computing time spent doing the rounds of the terminals; 40% of available computer time was not unheard of. The larger the installation, the more users and terminals, the more time was wasted.

To overcome this problem ‘Smart’ terminals were introduced along with dedicated IO (input/output) processing units. Smart terminal were so named for their ability to handle some relatively simple processing locally such as validation of user input fields and the ability to allow the user to move around a form adding data. When the user had completed the form the terminal would send back the results of the user input to the host as a block of data. These smart terminals are also called ‘block mode’ terminals.

System manufacturers soon realized that they could be more profitable by making their products unique and locking customers into their own product range. The net result was that each manufacturer had its own range of terminals which were largely incompatible with anyone else’s host system. The purchase of a particular mainframe computer system required the purchase of compatible terminals from the same manufacturer. As a consequence of this during the 1960s and onwards there existed a relatively large number of different computer companies each with their own unique and incompatible terminals.

However the end of the 1970s saw the reversal of this trend and the development of more standardized and general purpose machines from some of the computer industry’s newer players, most notably Digital Equipment Corporation (DEC). These machines used a standard serial connection along with standardized sets of characters and ‘escape sequences’, (commands were used to determine the text formatting, layout, and other display options on a terminal). This made it much simpler for other manufacturers to connect terminals and equipment to a host system.

Thanks largely to this openness and the size of the market that existed for terminals a number of companies emerged whose only business was to produce terminals for connection to host systems manufactured by others. These companies created terminals that could connect to any number of the available systems on the market and often had functionality that made them a cross between dumb and smart terminals without the costs of the latter. Terminals from manufacturers such as Televideo sported highly desirable and unique functionality that software developers took advantage of to enhance their own applications. In doing so software became dependent on hardware again, although in this case the terminal rather than the the host system. (Software could be run on different host systems so long as the application was able to be ‘ported’).

Finally, in the modern era the computer terminal has now almost entirely been replaced by the ubiquitous and multi functional PC. In the early days of the PC it was common to find a PC literally sitting alongside a computer terminal on the desk of the user. However it did not take long for this very poor use of valuable desk space and the duplication of investment in the PC and the Terminal to become an issue. The solution to this problem came in the form of a program that ran on the PC and mimicked the function of the terminal, the Terminal Emulator.

Terminal Emulation software put an end to the expense of purchasing and maintaining terminals, with their narrow and specialized functionality. Through a Terminal Emulator users are able to access host systems directly from their PC. Terminal Emulator software replicates the functionality and behavior of multiple terminal types and is available in versions which run a variety of devices found in the modern workplace, for example a hand held computer, a mobile phone or even through a web browser. In many cases Terminal Emulation software integrates with word processors, spreadsheets, email and so on, dramatically reducing the cost of host access while enhancing capability and presenting the end user with a familiar and modern interface to older technology.



Source by Scott Bickley

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