Display Devices

A display device or VDU (Video Display Unit) is an output device for presentation of information in visual. When the input information is supplied has an electrical signal, the display is called an electronic display.
Common applications for electronic visual displays are televisions or computer monitors.
All of the PCs that we use need to have some displays. Normally there are the standard monitors, but they now are available in various varieties like LCD, LED. The evolution of the displays has not just only made the space that they contain become less, but also has made them more efficient.

Common Terms

Pixel: In digital imaging, a pixel, pel, dots, or picture element is a physical point in a raster image, or the

smallest addressable element in an all points addressable display device; so it is the smallest controllable element of a picture represented on the screen. The address of a pixel corresponds to its physical coordinates. LCD pixels are manufactured in a two-dimensional grid, and are often represented using dots or squares, but CRT pixels correspond to their timing mechanisms .





Resolution: It Refers to the sharpness and clarity of an image. The term is most often used to describe monitors, printers, and bit-mapped graphic images. In the case of dot-matrix and laser printers, the resolution indicates the number of dots per inch. For example, a 300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line 1 inch long. This means it can print 90,000 dots per square inch.
For graphics monitors, the screen resolution signifies the number of dots (pixels) on the entire screen. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen.

 Aspect Ratio: The aspect ratio of an image describes the proportional relationship between its width and its height. It is commonly expressed as two numbers separated by a colon, as in 4:3 in display units.
 

Laser Printer

Laser printers are non impact printers work on the principle of static electricity i.e. atoms with opposite charges attract each other. The computer or digital camera sends the matter to be printed to the printer. This information is converted into dots by an internal processor.

The most important part of the printer is the photoreceptor , a revolving drum which is made of photoconductive material. This drum is given a positive charge. A laser beam is shot at it when there is a dot making that area negatively charged. The laser beam remains off when there is blank space. This is now exposed to laser toner which is positively charged. The positively charged toner pigments get attracted to the negatively charged areas of the electric drum. With one complete rotation, the drum is now covered with the required image.

Next the print media , say a paper, which is negatively charged is passed over the drum. The positively charged toner pigments now get attracted to the paper and the entire image is transferred to the paper. A fusing elementapplies heat and pressure to the paper; the toner melts and adheres to the paper.

Finally the drum is cleaned by mechanically scraping off of the toner and electrically charging the entire drum positive once more.

Laser printers have captured the black and white printing market. However color laser printers have not been able to match the quality of inkjet printers. Color laser printers use four separate color toner cartridges cyan, magenta, yellow, and black (CMYK).

Advantages

•  It has high speed of operation when compared with inkjets.

•  The diameter of the laser beam shot is constant, resulting in more precise pictures and no ink spillage problem like in inkjets.

•  No ink spillage problem that is possible in inkjets.

•  Though toner cartridges cost more than ink cartridges, but they last longer. Each cartridge yields around 2,500 to 10,000 pages. So the running cost is not high.

•  It is ideal for continuous text printing.

•  The color laser printers can print on a variety of media as the ink is fused into the paper. Control of the final heat and pressure applied on the paper can give a finish from matte or gloss finish.

 Disadvantages

•  High initial cost.

•  Toner cartridges are expensive as they include the electric drum, developer unit, ozone filter and fuser

•  The color printouts are not as good, not suitable for photography or high quality image printing.

•  Relatively heavier than an equivalent inkjet printer

Technical Features to be checked before buying a laser printer:

Inkjet Printer

An inkjet printer is non impact printer. It a computer peripheral that produces hard copy by spraying ink onto paper. A typical inkjet printer can produce copy with a resolution of at least 300 dots per inch ( dpi ). Some inkjet printers can make full color hard copies at 600 dpi or more. Many models include other devices such as a scanner , photocopier , and dedicated fax machine along with the printer in a single box.

In the inkjet printing mechanism, the print head has several tiny nozzles, also called jets. As the paper moves past the print head, the nozzles spray ink onto it, forming the characters and images. An inkjet printer can produce from 100 to several hundred pages, depending on the nature of the hard copy, before the ink cartridges must be replaced. There is usually one black ink cartridge and one so-called color cartridge containing ink in primary pigments (cyan, magenta, and yellow). Some inkjet printers use a single cartridge with cyan, magenta, yellow, and black ink. A few models require separate cartridges for each primary pigment, along with a black ink cartridge.

Inkjet Printing Process:
The main Components of an inkjet printer are as follows:

• Cartridges - The container that holds the ink. Some contain the print head.
• Print Head Assembly - Contains the nozzles for ink spraying.
• Rollers - Moves the paper as it's printing.
• Print Head Steppor Motor - Moves the cartridges and head back and forth. Some have a park motor to prevent the head assembly from moving when it's not being used.
• Paper Feed Steppor Motor - Powers the rollers.
• Belt - Connects the assembly to the motor.
• Stabilizer Bar - Makes sure the roller movement is consistent and the printing is precise.

 Some advantages
Initial Cost
Ink-Jet printers are one of the lowest cost products on the market. In the past, the quality of low inkjet printers have matched with its price.
Quality
Today you can create images or documents with high quality by Inkjet printers. They used to use blurry effect to the texts or images before but with the powerful technology now, you are able to create more effects so that your images are more vivid and have the best quality.
Space
Compare to laser printers, the ink jet printers have suitable size to put on the desk on your office or a small room in your home to serve to your work.
Time
Different from laser printer, the inkjet printer do not require time to heat the machine system before print. They have also shorter delay between the document being sent to print and the beginning of a print process.
Disadvantages
Cartridge Cost
You can buy a cheap inkjet printer first but with the replacement of the cartridges in a long time, the cartridge cost can exceed the machine cost.
Speed
You can only use ink-jet printer to create little volumes of documents only because inkjet printer is slower than laser one.
Ink
The replacement of cartridges causes some unexpected problems in the printing process. The most trouble we commonly face is when the printers are clogged with ink. There are cleaning cycles in inkjet printers to run but you must replace cartridges after used many times.
Moisture
After creating images or documents,we must wait until those dry. Sometimes it can delay our delivery process. There’s some risk if our documents smudge before drying.

Line Printers (Drum and Chain Printer)

Line Printers: They are known as line printers because they print one line at a time. Characteristics of a line printer:

1. Characters are raised on the drum or chain.
2. Different fonts cannot be used for printing.
3. High printing speed and quality.

There are two types of line printers: Drum printers and chain printers.

Drum Printers: In a drum printer characters are raised in a cylindrical drum. Values of all characters are stored in the printer buffer. When a character has to be printed, the printer sends the information to printer buffer.  Then, printer drum is rotated and when the code match is done the character is printed by striking the hammer.  There is a carbon ribbon in between the drum hammer and paper.  So, when the hammer strikes an impression is produced in the paper.

Chain Printers: Instead of a drum, chain with raised characters is used in these types of printers. Values of all characters are stored in the printer buffer. When a character has to be printed, the printer sends the information to printer buffer.  Then, printer chain is rotated and when the code match is done the character is printed by striking the hammer. There is a carbon ribbon in between the chain hammer and paper.  So, when the hammer strikes an impression is produced in the paper.

Daisy Wheel Printer

A daisy wheel printer is an early type of impact Printer invented in 1969 by David S. Lee at Diablo Data Systems. The printer uses a metal or plastic disk containing each of the letters, numbers, and other characters it supports. When something is printed, the printer rotates the disk to each character and then using a hammer strike each character into an ink ribbon to create the character on paper.

Daisy wheel printers were popular in the 1970s and 1980s, but are no longer used because of they have a low quality of print, are very slow, loud, and laser printers have come down in cost.
 Advantages:

1) It can print letter quality characters.

Disadvantages

1) Printing speed is slow.
2) It cannot print graphics.

Dot Matrix Printer

A Dot Matrix Printer or Impact Matrix Printer refers to a type of computer printer with a print head that runs back and forth on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced.

 Because the printing involves mechanical pressure, these printers can create carbon copies and carbonless copies. Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls). Facing the ribbon and the paper is a small guide plate pierced with holes to serve as guides for the pins. The moving portion of the printer is called the print head, and when running the printer as a generic text device it generally prints one line of text at a time.

Most dot matrix printers have a single vertical line of dot-making equipment on their print heads; others have a few interleaved rows in order to improve dot density. These machines can be highly durable, but eventually wear out. Ink invades the guide plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less accurate guidance to the printing wires.

Speed : Given in characters per second (cps), the speed can vary from about 50 to over 500 cps. Most dot-matrix printers offer different speeds depending on the quality of print desired.

Print Quality : Determined by the number of pins (the mechanisms that print the dots), it can vary from 9 to 24. The best dot-matrix printers (24 pins) can produce near letter-quality type, although you can still see a difference if you look closely.

Advantages :

1. can print on multi-part stationery or make carbon copies.

2. Impact printers have one of the lowest printing costs per page.

3. They are able to use continuous paper rather than requiring individual sheets.

4. The ink ribbon also does not easily dry out.

Disadvantages :

1. Impact printers are usually noisy.

2. They can only print low resolution graphics, with limited colour performance, limited quality and comparatively low speed.

3. They are prone to bent pins (and therefore a destroyed printhead) caused by printing a character half-on and half-off the label.

 

Printer

Printers are Output devices used to prepare permanent Output devices on paper. 

• Device that prints text and graphics in the same format and shape which is displayed on the screen connected via printer cable or USB cable.
• Transforms digitally stored documents, graphics, text data on paper/hard copy.
• Speed of printer is measured in printed pages per minute.
• Printers can be shared in the LAN, Wireless networks or Ethernets.
• New types of printers are combined with printing, scanning and fax in a single unit.

Printers can be divided into two main categories :

Impact Printers : In this hammers or pins strike against a ribbon and paper to print the text. This mechanism is known as electro-mechanical mechanism. They are of two types.

 

 

(i) Character Printer

(ii) Line Printer

Character Printer : It prints only one character at a time. It has relatively slower speed. Eg. Of them are Dot matrix printers. 
Line Printer : It prints one complete line at a time. Eg. Of them are Drum printers. 

Non-Impact Printers : There printers use non-Impact technology such as ink-jet or laser technology. There printers provide better quality of O/P at higher speed. These printers are of two types :

Recognition Devices

Character and mark recognition devices are scanners that are able to recognize special characters and marks. Essentially used for certain applications.

Types

MICR (Magnetic Ink Character Recognition):

• Used by banks to read numbers written on cheque.
• Special purpose machine reads character made of ink containing magnetized particles.

OCR (Optical Character recognition):

• Special preprinted characters that can be read by light source and changed into machine readable form.
• Used in department stores to read retail price tags by reflecting light.

OMR (Optical Mark Recognition):

• An OMR device senses the presence or absence of a mark such as pencil mark.
• Used to calculate or store multiple choice tests.
  
  
  

Bar Code Reader

• An electronic device used for reading printed bar codes.
• Consists of light source, lens, and light sensor for translating optical impulses into electrical ones.
• Also consists of decoder circuitry to analyze the barcode image data provided by sensor.
• This bar code identifies the product to the supermarket computer which has latest description and price.
• Computer automatically tells the electronic cash register the price.
• These are easy to use and widely used in electronic shops and malls.

Output Devices

An output device is any device used to send data from a computer to another device or user. Most computer data output that is meant for humans is in the form of audio or video. Thus, most output devices used by humans are in these categories. An output device is any peripheral that receives data from a computer, usually for display, projection, or physical reproduction.Examples include monitors, projectors, speakers, headphones and printers.

Output of processed data can be divided into two classes:

Hard Copy

Output that is in the form of print document, which can be read directly, long last and permanently stored. E.g. A word document containing text and images printed by the printer on a paper.

Soft Copy

Output that is in the form of metallic or audio form, which is cannot be read directly by the user. E.g. A collection of music files and folders on a CD.

Accordingly the output devices are classified as hard copy devices and soft copy devices.

• Hard Copy Devices : printers, fax machine, photographic output devices etc.
• Soft Copy Devices : monitors, data projectors, speakers etc.

Types

• Monitors
• Printers
• Data projectors
• Speakers
• EBook reader
• HDTV

Mouse, Joystick, Light pen

Mouse

Mouse is most popular pointing device. It is a very famous cursor-control device having a small palm size box with a round ball at its base which senses the movement of mouse and sends corresponding signals to CPU when the mouse buttons are pressed.
Generally it has two buttons called left and right button and a wheel is present between the buttons. Mouse can be used to control the position of cursor on screen, but it cannot be used to enter text into the computer.

Advantages

• Easy to use
• Not very expensive
• Moves the cursor faster than the arrow keys of keyboard.

Joystick

Joystick is also a pointing device which is used to move cursor position on a monitor screen. It is a stick having a spherical ball at its both lower and upper ends. The lower spherical ball moves in a socket. The joystick can be moved in all four directions.
The function of joystick is similar to that of a mouse. It is mainly used in Computer Aided Designing(CAD) and playing computer games.

Light Pen

Light pen is a pointing device which is similar to a pen. It is used to select a displayed menu item or draw pictures on the monitor screen. It consists of a photocell and an optical system placed in a small tube. When the tip of a light pen is moved over the monitor screen and pen button is pressed, its photocell sensing element detects the screen location and sends the corresponding signal to the CPU.

Input Devices

Those means or devices by which we feed data (any type) to computer. These devices have capability to convert that data in digital form i.e. in 0 & 1. Also known as peripherals and computer hardware.
Following are few of the important input devices which are used in a computer:

• Keyboard
• Mouse
• Joy Stick
• Light pen
• Track Ball
• Scanner
• Graphic Tablet
• Microphone
• Magnetic Ink Card Reader(MICR)
• Optical Character Reader(OCR)
• Bar Code Reader
• Optical Mark Reader(OMR)

Keyboard

Keyboard is the most common and very popular input device which helps in inputting data to the computer. The layout of the keyboard is like that of traditional typewriter, although there are some additional keys provided for performing additional functions.
Keyboards are of two sizes 84 keys or 101/102 keys, but now keyboards with 104 keys or 108 keys are also available for Windows and Internet.
The keys on the keyboard are as follows:

Sr.No	Keys	Description
1	Typing Keys	These keys include the letter keys (A-Z) and digit keys (0-9) which generally give same layout as that of typewriters.
2	Numeric Keypad	It is used to enter numeric data or cursor movement. Generally, it consists of a set of 17 keys that are laid out in the same configuration used by most adding machines and calculators.
3	Function Keys	The twelve function keys are present on the keyboard which are arranged in a row at the top of the keyboard. Each function key has unique meaning and is used for some specific purpose.
4	Control keys	These keys provide cursor and screen control. It includes four directional arrow keys. Control keys also include Home, End, Insert, Delete, Page Up, Page Down, Control(Ctrl), Alternate(Alt), Escape(Esc).
5	Special Purpose Keys	Keyboard also contains some special purpose keys such as Enter, Shift, Caps Lock, Num Lock, Space bar, Tab, and Print Screen.

SRAM vs DRAM

SRAM vs DRAM

There are two types of Random Access Memory or RAM, each has its own advantages and disadvantages compared to the other. SRAM (Static RAM) and DRAM (Dynamic RAM) holds data but in a different ways. DRAM requires the data to be refreshed periodically in order to retain the data. SRAM does not need to be refreshed as the transistors inside would continue to hold the data as long as the power supply is not cut off. This behavior leads to a few advantages, not the least of which is the much faster speed that data can be written and read.

1. SRAM is static while DRAM is dynamic
2. SRAM is faster compared to DRAM
3. SRAM consumes less power than DRAM
4. SRAM uses more transistors per bit of memory compared to DRAM
5. SRAM is more expensive than DRAM
6. Cheaper DRAM is used in main memory while SRAM is commonly used in cache memory