Fundamentals of Computers I-33
Non-impact printers
Unlike impact printers, a non-impact printer forms characters and images without making direct
physical contact between printing mechanism and paper. In this printer, the print head does not make
contact with the paper, and no inked ribbon is required. Ink can be sprayed against the paper and then
heat and pressure are used to fuse a fine black powder into the shape of a character. The major technolo-
gies competing in the market of non-impact printers are ink-jet and laser. Some characteristics of non-
impact printers are as follows:
• They are faster because they have fewer moving parts.
• They are quieter because there is no striking mechanism involved and only few moving parts are
used.
• They possess the ability to change typefaces automatically.
• They produce high-quality graphics.
• They cannot print carbon copies.
41. Explain laser printer and its working concept in detail.
Ans: A laser printer provides the highest quality text and images for personal computers today. It is
a very fast printer, which operates on the same principle as that of a photocopy machine. Most laser
printers can print text and graphics with a very high quality resolution. They are also known as ‘page
printers’ because they process and store the entire page before they actually print it. They produce sharp,
crisp images of both text and graphics, providing resolutions from 300 to 2,400 dpi. Today, the resolu-
tion of most printers is 600 dpi. They are quiet and fast, able to print 4–32 text-only pages per minute
for individual microcomputers and up to 200 pages per minute for mainframes. Laser printers can print
in excess of 2000 lines per minute. Furthermore, they can print in different fonts, that is, type styles and
sizes. Laser printers are often faster than ink-jet printers but are more expensive to buy and maintain than
the other printers. The cost of these printers depends on a combination of costs of paper, toner replace-
ment and drum replacement. These printers are useful for volume printing because of their speed. The
working of laser printer is described as follows:
Working of a Laser Printer
The core component of laser printing system is the photoconductive drum. A rotating mirror inside
the printer causes the beam of a laser to sweep across the photoconductive drum. Initially, the beam
of laser charges the photoconductive drum positively. When the charged photoconductor is exposed
to an optical image through a beam of light to discharge, a latent or invisible image is formed. At the
point where the laser strikes the surface of drum, it creates a dot of positive charge. These points are
represented by a black dot, which will be printed on the paper. After this, the printer coats the drum
with a container, which contains a black powder called ‘toner’. This toner is negatively charged, and
so it clings to the positive areas of the drum surface. When the powder pattern gets fixed, the drum is
rotated and the paper is fed into the drum surface via a pressure roller. This pressure roller transfers the
black toner onto the paper. Since the paper is moving at the same speed as the drum, the paper picks
up the image pattern precisely. Finally, the printer passes the paper through the fuser, a pair of heated
rollers. As the paper passes through these rollers, the loose toner powder gets melted and fuses with
the fibres in the paper. The paper is then brought out of the printer. Figure 1.7 illustrates the working
of laser printer.
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I-34 Computer Fundamentals
Paper exit
Laser
scanning
unit
Mirror
Toner
coated
roller
Toner
hopper
Fuser
Paper Tray
Charging
electrode
Photoreceptor
drum
Figure 1.7 Working of a Laser Printer
42. What is the role of visual display unit? Also discuss the types of monitors.
Ans: The monitor, also known as ‘visual display unit’ (‘VDU’), is the most frequently used
output device for producing soft-copy output. A computer monitor is a TV-like display attached to
the computer on which the output can be displayed and viewed. The computer monitor can either
be a monochrome display or a colour display. A monochrome screen uses only one colour (usually
white, green, amber or black) to display text on contrasting background. Colour screens commonly
display 256 colors at one time from a selection of over 2,56,000 choices. Monitors are available
in various sizes like 14, 15, 17, 19 and 21 inches. The size of the display is described based on
two parameters, namely, aspect ratio and screen size. ‘Aspect ratio’ is the ratio of the width of the
display screen to the height, that is, the ratio of vertical points to the horizontal points necessary to
produce equal-length lines in both directions on the screen. Generally, computer displays have an
aspect ratio of 4:3. Like televisions, ‘screen sizes’ are normally measured diagonally (in inches),
the distance from one corner to the opposite corner. The description of various types of monitors
is as follows:
• Cathode ray tube (CRT): Nowadays, most computer monitors are based on cathode ray tube
(CRT) technology. The basic operation of these tubes is similar to that in television sets. The pri-
mary components in a CRT are the heated metal cathode and a control grid. Heat is supplied to the
cathode by directing a current through a coil of wire, called the ‘filament’, inside the cylindrical
cathode structure. This causes electrons to be boiled off the hot cathode surface. In the vacuum
inside the CRT envelope, the free, negatively charged electrons are then accelerated toward the
phosphor coating by a highly positive voltage. The accelerating voltage can be generated with a
positively charged metal coating on the inside of the CRT envelope near the phosphor screen, or
an accelerating anode can be used.
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Fundamentals of Computers I-35
• Liquid crystal display (LCD): With the widespread use of smaller computers like PDAs and
laptops, a new type of display liquid crystal display (LCD) has made a big impact on computer
market. LCD screens have been used since long on notebook computers but are also becoming
popular as a desktop monitor. The term liquid crystal sounds like a contradiction. We generally
conceive a crystal as a solid material such as quartz and a liquid as water-like fluid. However,
some substances can exist in an odd state that is semi-liquid and semi-solid. When they are in this
state, their molecules tend to maintain their orientation like the molecules in a solid, but also move
around to different positions like the molecules in a liquid. Thus, liquid crystals are neither a solid
nor a liquid. Manufacturers use this amazing ability of liquid crystals to display images.
• Plasma display: A plasma display (also known as ‘thin-panel’) is constructed by filling a gas
(Neon or Xenon) between the two glass plates. One glass plate consists of vertical conductors
and the other consists of horizontal conductors. When the voltage is applied to the pair of
horizontal and vertical conductors, the gas at the intersection of two conductors glows. The
advantage of plasma display is that it has the capability of producing more than 16 million
colours and is lighter and less bulky than CRT. However, it is heavier than LCD display and
requires more power.
• Thin-film electroluminescent display: This display is similar to the plasma display except the
fact that the space between the glass plates is filled with phosphorescent substance (usually zinc
sulphide doped with manganese) instead of gas. When the high voltage is applied to the crossing
conductors, the phosphoric substance at the intersection of two conductors becomes conductor and
generates the electrical energy. This energy is absorbed by the manganese atoms and then released
as a spot of light. The main problem with thin-film electroluminescent displays is that they require
more power.
Multiple-choice Questions
1. GIGO stands for .
(a) Garbage in garbage out (b) Gigabyte in gigabyte out
(c) Get in get out (d) None of the above
2. Modifications in sand tables resulted in a device known as .
(a) Computer (b) Pascaline (c) Abacus (d) All of the above
3. Which computers are based on vacuum tube technology?
(a) First generation (b) Second generation
(c) Third generation (d) Fourth generation
4. Which type of computer you will most likely to encounter at the department of motor vehicles?
(a) Smart phone (b) Mainframe
(c) Super computer (d) Mini computer
5. Which of these is an example of hand-held computer?
(a) RAM (b) PDA (c) BUS (d) CMOS
6. Stylus is used to input data in
(a) Laptop (b) Desktop (c) PDA (d) None of these
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I-36 Computer Fundamentals
7. Which of the following acts as the primary controlling mechanism for the computer’s hardware?
(a) RAM (b) CPU (c) Operating system (d) CD ROM
8. Which of these is not a part of CPU?
(a) CU (b) ALU (c) L2 cache (d) L3 cache
9. ALU is a part of .
(a) Memory (b) CPU (c) Input device (d) Output device
10. Which of the following caches holds the most recently used data or instructions?
(a) L1 (b) L2 (c) L3 (d) L4
11. The register which contains the instructions that are to be executed is known as .
(a) Index register (b) MAR (c) Instruction register (d) MBR
12. Which one of the following units represents the largest amount of data?
(a) KB (b) GB (c) TB (d) MB
13. Which of the following devices stores the instructions that help the computer start up?
(a) RAM (b) ROM (c) Monitor (d) CD ROM
14. Memory that loses data when the power is turned off is considered as .
(a) Volatile memory (b) Static memory
(c) Dynamic memory (d) Refreshed memory
15. Which of the following is not used as secondary storage?
(a) Semiconductor memory (b) Magnetic drum
(c) Magnetic disk (d) Magnetic tape
16. An example for magnetic storage device is .
(a) CD ROM (b) Hard disk (c) Flash memory (d) DVD
17. A laser printer’s speed is measured in .
(a) cps (b) ppm (c) dpi (d) lpm
18. A computer resolution is determined by .
(a) Monitor (b) Video controller (c) CPU (d) System unit
19. is also known as thin-panel.
(a) Plasma display (b) LCD (c) CRT (d) None of the above
Answers
1. (a) 2. (c) 3. (a) 4. (b) 5. (b) 6. (c) 7. (c) 8. (d) 9. (b) 10. (a)
11. (c) 12. (c) 13. (b) 14. (a) 15. (a) 16. (b) 17. (c) 18. (b) 19. (a)
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