Computer output, hard copy

The networking of personal computers has continued and has enabled the sharing of expensive hard-copy output devices and other peripherals and has provided the significant benefit of faciUtating the transfer of data between computers. Joint authorship of technical articles is a quick and easy process with networked computers. The interappHcation communication that today links appHcations within a single computer will transparentiy link appHcations on networked computers. Voice-annotated documents are already available. 

Printers and their operation are the subject of Chapter 7 (and also about half of the troubleshooting chapter. Chapter 10), so we ll just briefly talk about the different types. There are four major types of printing devices used to get computer output into hard copy (paper copies). They are impact, sprayed-ink, electrophotographic (EP), and plotters. 

All microcomputers have at least one output device, usually a monitor screen with a printer as a second output device giving hard copy. On desk-top computers, the screen is usually a cathode ray tube, while on portable computers liquid crystal or gas plasma screens are used. EEU"ly screen displays simply emulated the teletypes used at that time to communicate with mainframe computers. These glass teletypes displayed only characters. The computer simply sent a stream of bytes to the output device. The device was electronically connected to the microcomputer in such a way that from the microprocessor s point of view the output device resembled one or more memory locations. Whenever the microprocessor wrote into these memory locations, characters appeared on the screen. The convention used on all modern microcomputers when converting from bytes to characters is the American Standard Code for Information Interchange (ASCII). 

Appropriate controls should be exercised over computer or related systems to assure that changes in master production and control records or other records are instituted only by authorised personnel. Input to, and output from the computer or related system, of formulae or other records or data shall be checked for accuracy. A backup file of data entered into the computer or related system shall be maintained, except where certain data such as calculations are eliminated by computerisation or other automated processes. In such instances either a written record of the programme (source code) shall be maintained or the system should be validated. Hard copy or alternative systems, such as duplicates, tapes, or microfilm, designed to assure that backup data are exact and complete and that it is secure from alteration, inadvertent erasure or loss, shall be maintained. 

The first problem to be solved is that of man- nachine communication. Corey, Wipke and others have developed a system by which the chemist feeds in a structure by drawing a standard two-dimensional structural formula using an electrostatic tablet (Rand tablet) and a Rand pen. The computer communicates with the chemist by displaying conventional structural formulae on a cathode ray tube. Provision is also made for hard copy output using a plotter. As emphasized by Corey and Wipke 8.5) this allows for cui interactive relationship between the chemist and the computer. 

Almost any computer requires one or more output ports that permit the CPU to communicate the result of its processing to the outside word. The output may go to a display, for use by a human operator to a peripheral device that produces hard copy, such as a line printer or to a peripheral storage device, such as a magnetic tape unit or the output may constitute process control signals that direct the operations of another system, such as an automated assembly line. Like input ports, output ports are addressable. The input and output ports together permit the processor to interact with the outside world. Data exchanges take place with external or peripheral devices via an I/O register. 

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