Лекция: OUTPUT DEVICES. PRINTERS
Several devices are used for outputting information from the computer, but printers are sure to be the most commonly used output devices and to be components of almost all computer systems. We consider printers to provide information in a permanent and much more human-readable form than any other means. Printers vary greatly in performance and design.
We will classify printers as character printers, line printers and page printers in order to identify three different approaches to printing, each with a different speed range. In addition, printers can be described as either impact or non-impact. Printers that use electromechanical mechanisms that cause hammers to strike against a ribbon and the paper are called impact printers. Non-impact printers do not hit or impact a ribbon to print.
Character printers print only one character at a time. A typewriter is an example of a character printer. Character printers are the type used with literally all microcomputers as well as on computers of all sizes whenever the printing requirements are not large. Character printers may be of several types. A letter-quality printer is a character printer which produces output of typewriter quality. Such a printer has speeds ranging from 10 to 50 characters per second. Dot-matrix printers form each character as a pattern of dots. These printers are stated to have a lower quality of type. But they are generally faster printers than the first ones — in the range of 50 to 200 characters per second. One of the newest types of character printer is the ink-jet printer. It sprays small drops of ink onto paper to form printed characters. The ink has a high iron content, which is affected by magnetic fields of the printer. These magnetic fields cause the ink to take the shape of a character as the ink approaches the paper.
Line printers are electromechanical machines used for high-volume paper output on most computer systems. Their printing speeds are such that to an observer they appear to be printing a line at a time. They are impact printers. The speeds of them vary from 100 to 2500 lines per minute.
Page printers are high-speed non-impact printers. Their printing rates are so high that output appears to emerge from the printer a page at a time. A variety of techniques are used in the design of page printers. These techniques, called electrophotographic techniques, have developed from the paper copier technology. Laser-beam printers use a combination of laser beam and electrophotographic techniques to create printer output at a rate equal to 18000 lines per minute.
Answer the following questions:
1. What are the three types of printers? 2. What is a letter-quality printer? What is a dot-matrix printer? 3. What type of printer is the most common with microcomputer systems? 4. What is an impact printer? Give an example. 5. What is a non-impact printer? Give examples. 6. How do you distinguish between a letter-quality printer and a dot-matrix printer? Which of these printers is slower? 7. What types of character printers do you know? 8. How are printed characters formed by means of an ink-jet printer? 9. What are the main types of a line printer? Which of them is faster? 10. What techniques are used in the operation of page printers?