The document discusses three primary computer storage devices: magnetic disks, tape recorders, and CRTs. Magnetic disks use rotating platters to store data magnetically and allow for quick read/write access times. Tape recorders also store data magnetically on tape and revolutionized radio broadcasting and music recording industries. CRTs use an electron gun and phosphor screen to display output and were commonly used as computer monitors.

1. Magnetic Disk
• The primary computer storage device. Like tape, it is
magnetically recorded and can be re-recorded over and
over. Disks are rotating platters with a mechanical arm
that moves a read/write head between the outer and inner
edges of the platter's surface. It can take as long as one
second to find a location on a floppy disk to as little as a
couple of milliseconds on a fast hard disk.
• Tracks and Spots
The disk surface is divided into concentric tracks (circles
within circles). The thinner the tracks, the more storage.
The data bits are recorded as tiny magnetic spots on the
tracks. The smaller the spot, the more bits per inch and
the greater the storage.
• Example – Hard disk in computer
Floppy Disk

2. Tape Recorders
• An audio tape recorder, tape deck, reel-to-reel tape
deck, cassette deck or tape machine is an audio
storage device that records and plays back sounds, including
articulated voices, usually using magnetic tape, either
wound on a reel or in a cassette, for storage.
• The use of magnetic tape for sound recording originated
around 1930. Magnetisable tape revolutionized both the
radio broadcast and music recording industries.
• The alternative recording technologies of the
era, transcription discs and wire recorders, could not provide
anywhere near this level of quality and functionality.

3. Tape Recorders
• In its present day form, it records a
fluctuating signal by moving the tape across
a tape head that polarizes the magnetic
domains in the tape in proportion to the audio
signal.
• It gave artists and producers the power to record
and re-record audio with minimal loss in quality
as well as edit and rearrange recordings with ease.
• However, as of the first decade of the 21st
century, analog magnetic tape is largely being
replaced by digital recording technologies for
most sound recording purposes

4. CRT

5. Structure of Cathode Ray Tube
• Etymology: “Cathode rays” in a vacuum tube. Cathode rays are high
energy electrons emitted from the heated cathode (-) of a vacuum
tube

6. How Does it Work
• Electron gun is weak particle accelerator (only electrons(-)).
• Aims electrons at phosphor screen where they light up the image
• Small heater heats cathode (-), emits electron cloud that is focused
into an electron beam by two anodes(+): accelerating anode and
focusing anode.
• Black-and-white monitors only have one electron gun; color monitors
have three (RGB).

7. Variations of CRTs
• Metal screen filled with holes sitting just behind phosphor layer.
Electron guns each send beam through hole to a single pixel triad of
tube’s phosphor layer.
• Aperture Grill - Looks kind of like a grill; with lines jutting down the
screen packed together in strips
• Shadow Mask – - packed together in clusters. If you look closely, you
can see little individual dots, known as pixels

8. Advantages of CRT
• The cathode rayed tube can easily increase the monitor’s brightness by reflecting the light.
• They produce more colours
• The Cathode Ray Tube monitors have lower price rate than the LCD display or Plasma display.
• The quality of the image displayed on a Cathode Ray Tube is superior to the LCD and Plasma
monitors.
• The contrast features of the cathode ray tube monitor are considered highly excellent.

9. Disadvantages of CRT
• They have a big back and take up space on desk.
• The electromagnetic fields emitted by CRT monitors constitute a health hazard to the functioning
of living cells.
• CRTs emit a small amount of X-ray band radiation which can result in a health hazard.
• Constant refreshing of CRT monitors can result in headache.
• CRTs operate at very high voltage which can overheat system or result in an implosion
• Within a CRT a strong vacuum exists in it and can also result in a implosion
• They are heavy to pick up and carry around

10. Digital Plotter and Printer
• The plotter is a computer printer for printing vector graphics. In the
past, plotters were used in applications such as computer-aided design,
though they have generally been replaced with wide-format
conventional printers.
• A plotter gives a hard copy of the output. It draws pictures on paper
using a pen. Plotters are used to print designs of ships and machines,
plans for buildings and so on.
• Digital printing refers to methods of printing from a digital-based
image directly to a variety of media. It usually refers to professional
printing where small-run jobs from desktop publishing and other digital
sources are printed using large-format and/or high-volume laser
or inkjet printers. Digital printing has a higher cost per page than more
traditional offset printing methods.

11. Some of the more common printing technologies are:
• blueprint – and related chemical technologies
• daisy wheel – where pre-formed characters are applied individually
• dot-matrix – which produces arbitrary patterns of dots with an array
of printing
• line printing – where formed characters are applied to the paper by
lines
• heat transfer – such as early fax machines or modern receipt printers
that apply heat to special paper, which turns black to form the
printed image
• inkjet – including bubble-jet, where ink is sprayed onto the paper to
create the desired image
• electrophotography – where toner is attracted to a charged image and
then developed
• laser – a type of xerography where the charged image is written
pixel by pixel using a laser
• solid ink printer – where cubes of ink are melted to make ink or
liquid toner

12. LCD

13. LCD History
• Liquid crystals were first discovered in 1888 by Austrian
botanist Friedrich Reinitzer.
• Melt cholesterol-like substance.
• When cooled, the liquid turned blue before finally
crystallizing.
• RCA made the first experimental LCD in (1968).
• Manufacturers have been developing creative variations
and improvements since on LCDs.

14. LCD Technology
• Used for displays in notebooks, small computers,
pagers, phones and other instruments.
• Uses a combination of fluorescent-based backlight,
color filters, transistors, and liquid crystal to create
and illuminate images.
• Until recently, was only used on notebook computers
and other portable devices.
• In 1997, manufactures began to offer full size LCD
monitors as alternatives to CRT monitors.

15. Advantages of LCDs
• Power Consumption and Radiation Emission
• Consume less energy and more durable
• A typical CRT losses approximately 50% of its brightness
after 10,000 hours. An LCD bulb will maintain its brightness
anywhere from 25,000 to 50,000 hours.
• LCD consumes fewer watts than a CRT. LCD will use an
average 30 watts compared to 120 watts for the CRT.
• Can reduce electric bill by 40-85%.
• Uses a combination of fluorescent-based backlight, color
filters, transistors, and liquid crystal to create and illuminate
images. It blocks light rather emit light

16. Advantages of LCDs
• Power Consumption and Radiation Emission
• Does not emit Radiation
• Not subject to Electromagnetic Interference
• Viewing
• Cause less eyestrain
• Does not flicker or glare

17. How does it work & display
• Liquid crystal displays work by the tiny pixels on the screen
showing more than 20,000,000 colours an LCD screen is a
multilayered, sideways sandwich.
• A fluorescent light source, known as the backlight. This light
passes through the first of two polarizing filters.
• The polarized light then passes through a layer that contains
thousands of liquid crystal pixels arrayed in tiny containers
called cells. The cells are, in turn, arrayed in rows across the
screen; one or more cells make up one pixel.
• Electric leads around the edge of the LCD create an electric
field that twists the crystal molecule, which lines the light
up with the second polarizing filter and allows it to pass
through it.

18. Advantages of LCD
• The sharpness of a LCD display is at maximum tweakness.
• Zero geometric distortion at the native resolution of the panel.
• High peak intensity produces very bright images. Best for brightly lit environments.
• Screens are perfectly flat.
• Thin, with a small footprint. Consume little electricity and produce little heat
• The LCD display unit is very light and can be put anywhere or moved anywhere in the house.
• Lack of flicker and low glare reduce eyestrain.

19. Disadvantages of LCD
• After a while the LCD display the some of the pixels will die you will see a discoloured spot on a black spot
on the display.
• The cost of a LCD is considerably at a high price.
• The LCD display will have slow response times.
• The LCD display has a fixed resolution display and cannot be changed.
• LCDs use analog interface making careful adjustment of pixel tracking/phase in order to reduce or
eliminate digital noise in the image.
• The viewing angle of a LCD display is very limited due to the Automatic pixel tracking/phase
controls.
•

20. CRO

21. CRO - Functional Units
a) Electron Gun
b) Evacuated Tube
c) Deflecting System
d) Time Base
e) Trigger Circuit

22. Electron Gun

23. Evacuated Tube
• Vacuum space
• Screen
• Graphite inner wall
• Shielded from electric and magnetic fields

24. Deflecting System
• X-plates
• Y-plates
• X and Y Deflection Amplifiers
• X-shift Control
• Y-shift Control
• Sensitivity Control

25. Time Base
• Sawtooth potential difference
• Time period control

26. Trigger Circuit
• Maintain a stable trace
• Trig level control
• Trigger time base
• automatic triggering

27. USES OF CRO
a) Voltmeter
b) Display of waveforms
c) Measurement of short time intervals
d) Measurement of frequency
e) Display of phase relationship
f) Comparison of frequencies

28. LIGHT EMITTING DIODES

29. A light emitting diode (LED) is essentially a PN junction opto-semiconductor that emits
a monochromatic (single color) light when operated in a forward biased direction.
LEDs convert electrical energy into light energy. They are frequently used as "pilot"
lights in electronic appliances to indicate whether the circuit is closed or not.
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30. About LEDs (1/2)
The most important part of a light emitting diode (LED) is the semi-conductor
chip located in the center of the bulb as shown at the right. The chip has two regions
separated by a junction. The p region is dominated by positive electric charges, and the n
region is dominated by negative electric charges. The junction acts as a barrier to the
flow of electrons between the p and the n regions. Only when sufficient voltage is
applied to the semi-conductor chip, can the current flow, and the electrons cross the
junction into the p region.
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31. How Does A LED Work
When sufficient voltage is applied to the chip
across the leads of the LED, electrons can move easily in
only one direction across the junction between the p and n
regions.
In the p region there are many more positive than
negative charges.
When a voltage is applied and the current starts to
flow, electrons in the n region have sufficient energy to
move across the junction into the p region.
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32. How Does A LED Work
Each time an electron recombines with a positive charge, electric
potential energy is converted into electromagnetic energy.
For each recombination of a negative and a positive charge, a quantum
of electromagnetic energy is emitted in the form of a photon of light with a
frequency characteristic of the semi-conductor material (usually a combination
of the chemical elements gallium, arsenic and phosphorus)..
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33. Applications
• Sensor Applications
• Mobile Applications
• Sign Applications
• Automative Uses
• LED Signals
• Illuminations
• Indicators
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34. DOT MATRIX DISPLAY
• A dot-matrix display is a display device used to display information
on machines, clocks, railway departure indicators and many other
devices requiring a simple display device of limited resolution.
• The display consists of a dot matrix of lights or mechanical indicators
arranged in a rectangular configuration (other shapes are also
possible, although not common) such that by switching on or off
selected lights, text or graphics can be displayed. A dot matrix
controller converts instructions from a processor into signals which
turns on or off lights in the matrix so that the required display is
produced.

35. Usual resolutions:
•128×16 (Two lined)
•128×32 (Four lined)
•128×64 (Eight lined)
Usual character resolutions:
•A common size for a character is 5×7 pixels, either separated with blank lines with no dots (in most textonly displays), or with lines of blank pixels (making the real size 6x8). This is seen on most graphic
calculators, such as Casio calculators or TI-82 and superior.
•A smaller size is 3×5 (or 4x6 when separated with blank pixels). This is seen on the TI-80 calculator as a
"pure", fixed-size 3×5 font, or on most 7×5 calculators as a proportional (1×5 to 5×5) font. The
disadvantage of the 7×5 matrix and smaller is that lower case characters with descenders are not practical.
A matrix of 11×9 is often used to give far superior resolution.
•Dot matrix displays of sufficient resolution can be programmed to emulate the customary sevensegment numeral patterns.