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Plotters are printers that are used to print graphical output on paper. They use a single color or multicolor pens to draw pictures such as blueprints, graphs, drawings, charts, maps, etc.

Liquid Crystal Display/Diode.

Cathode Ray Tube.

Programmable Read-Only Memory

Memory is classified as Primary memory and Secondary memory.

Monitor resolution is the measurement of the number of pixels that a computer display or monitor, can show at one time.

Print resolution is measured in terms of number of dots per inch (dpi)

The term “pixels” is short for picture elements, and a pixel is the smallest element of an image.

It is a pen-shaped input device used to select objects on a display screen. It uses a light pen to move the pointer and select any object on the screen by pointing at the object.

1. Volatile memory:

In volatile memory, information written on it can be accessed as long as the power is on. As soon as the power is off, it can not be accessed because data is erased automatically and made empty.

2. Non-volatile memory:

The information stored in it is not lost even if the power supply goes off. It’s used for the permanent storage of information.

Scanner is an input device that converts the document image into digital form so that it can be fed into the computer.

Non-impact printers form characters and images without direct physical contact between the printing mechanism and the paper.

Ink-jet printer and Laser printer.

Primary Memory:

• Primary memory is smaller in storage capacity. 
• Primary memory is costly but very fast in read/write data.
• It is accessible by the CPU only.

Secondary Memory:

• They can store a very large volume of data.
• They are relatively cheaper but slower in read/write data.
• They are accessible to the user.

Primary memory is also known as the main memory, in which data is stored for quick access by the CPU. It allows very fast access to data. It is relatively costly. A CPU has three parts namely primary memory, arithmetic logic unit (ALU) and control unit. Primary memory is fast and costly as compared to secondary storage.

Daisy wheel printer and dot matrix printer.

Bar Code Reader/Recognition.

Bar codes are a set of black lines of different thicknesses with spaces between them representing numeric characters. Bar code readers are used to input data from bar codes. Most products in departmental stores/ bookshops have bar codes on them. Bar code readers work by shining a beam of light on the lines that make up the bar code and detecting the amount of light that is reflected back.

The joystick is an input device and is a vertical stick which moves the graphic cursor in the direction the stick is moved.

RAM (Random Access Memory) and ROM (Read Only Memory) are the two types of primary memory.

The different types of ROM are PROM, EPROM, EEPROM.

Binary  Digit.

Magnetic Ink Character Reader enables special characters printed in magnetic ink to be read and input rapidly to a computer. MICR is used extensively in banking because magnetic-ink characters are difficult to forge and are therefore ideal for marking and identifying cheques.

Optical Character. Recognition (OCR) is an input device that is used to scan the printed/ handwritten text materials into computer-readable text making it easy to edit and store. It is used to read the cheque numbers in the banks and millions of magazines and letters are sorted every day by OCR machines.

1. A cathode ray tube (CRT) monitor is an analog computer display with a large, deep casing. This type of monitor uses streams of electrons that activate dots or pixels on the screen to create a full image.

2. An LCD monitor is a thin, light computer monitor that displays images through the use of a liquid crystal display. LCD screens are found in most laptop computers as well as in flat-panel monitors.

3. ATFT monitor uses thin-film transistor technology in an LCD display. Nearly all LCD monitors today use TFT technology. Light-emitting diode (LED) screens are liquid crystal display screens that use LED backlighting

Optical Character Reader/Recognition

The different types of RAM are Static RAM and Dynamic RAM

8 bits make one byte.

Static RAM:

• SRAM uses six transistors for each memory cell.
• SRAM doesn’t need a refresher circuit.
• SRAM is costlier and used for the smaller and faster cache memory.

Dynamic RAM:

• DRAM uses a single capacitor and a transistor for each memory cell
• DRAM requires to be refreshed periodically.
• DRAM is cheaper and slower and is used for the large main memory.

Dot-matrix printer is an impact printer that prints text and graphics on the paper by using tiny dots to form the shapes. It uses a set of metal pins known as print head to strike an inked printer ribbon and produce dots on the paper. These combinations of dots give the desired shape on the paper. Generally, they print with a speed of 50 to 500 characters per second as per the quality of the printing is desired. The quality of the print is determined by the number of pins used (varying from 9 to 24).

The mouse is an input device used to point to a particular place on the screen. It sends the movement of itself in x and y coordinates to the system and selects in order to perform one or more actions. It can be used to select menu commands, size windows, start programs, etc. The most conventional kind of mouse has two buttons on top: the left one being used more often.

1. Mouse Actions:

(i) Left-click : used to select an item.

(ii) Double click: used to start a program or open a file.

(iii) Right-click: usually used to display a set of commands.

2. Drag and Drop:

It allows you to select and move an item from one location to another. To achieve this, place the cursor over an item on the screen, click the left mouse button and while holding the button down, move the cursor to where you want to place the item, and then release it. There are two main kinds of mouses. A ball-type mouse uses a rubber ball for rolling and an optical mouse by bouncing a light beam off to work desk or mouse, pad.

3. The working principle of the ball computer mouse:

As the user moves it across the desk, the ball rolls under its own weight and pushes against two plastic rollers linked to thin wheels. One of the wheels detects movements in an up-and-down direction (like the y-axis on graph/ chart paper); the other detects side-to-side movements (like the x-axis on graph paper).

4. The working principle of the optical mouse:

An optical mouse shines a bright light down onto the desk or pad from an LED, mounted on the bottom of the mouse. The light bounces straight back up off the desk into a photocell, also mounted under the mouse, a short distance from the LED. The photocell lens magnifies the reflected light, so the mouse can respond more precisely to hand movements. As the mouse moves around the pattern of reflected light changes and the chip inside the mouse identifies the movement. This movement is converted into signals and sent to the computer to move the cursor accordingly.

The monitor displays the video and graphics information generated by the computer through the video card. Monitors are very similar to televisions but usually display information at a much higher resolution. Monitors come in two major types – LCD or CRT. CRT monitors look much like old-fashioned televisions and are very bulky in size. LCD monitors are much thinner, use less energy, and provide a greater graphics quality.

1. CRT monitor:

A cathode ray tube (CRT) monitor is an analog computer display with a large, deep casing. This type of monitor uses streams of electrons that activate dots or pixels on the screen to create a full image. As the electrons hit the phosphors on the CRT, the phosphor will glow with certain intensities. As a new line begins, the gun will then begin at the left and continue right. The gun will repeat this process sometimes thousands of times until the screen has been completely drawn line by line. Once the phosphors on the CRT have been hit with an electron they will only glow for a short period of time; because of this, the CRT must be refreshed, which means the process will be repeated as explained above.

2. LCD Monitors:

An LCD monitor is a thin, light computer monitor that displays images through the use of a liquid crystal display. LCD screens are found in most laptop computers as well as in flat-panel monitors. The display is created by sending various voltages of electricity to cells of liquid crystal causing the liquid crystal to untwist at the rate of electricity applied, generating 64 different shades per cell.

3. A TFT monitor:

It uses thin-film transistor technology in an LCD display. Nearly all LCD monitors today use TFT technology.

4. Light-emitting diode (LED):

Light-emitting diode (LED) screens are liquid crystal display screens that use LED backlighting.

5. Pixel resolution:

A pixel (short for picture element,) is one of the many tiny dots that make up the representation of a picture in a computer’s memory. The pixel counts are referred to as resolution, is described Pixel resolution with a set of two positive integer numbers, where the first number is the number of pixel columns (width) and the second is the number of pixel rows (height), for example as 640 by 480.

6. Monitor Size: 

The size of the monitors is measured diagonally and comes in various sizes. The sizes are 12 inch, 14 inch, 15.6 inch, 18.5 inch, 19.5 inch, 21.5 inch, and 23 inch, etc.,

Optical Mark Recognition (OMR) is the technology of electronically taking out data from marked fields, such as oval shades and fill-in fields, on printed forms. OMR technology scans a printed form and reads predefined positions and records where marks are made on the form. This technology is useful for applications in which large numbers of hand-filled forms need to be processed quickly and with greater accuracy, such as questionnaires, and academic exams. A common OMR application is the use of “oval sheets” for multiple-choice tests used by schools and colleges.

The student indicates the answer on the test by filling in the corresponding oval, and the form is fed through an optical mark reader, a device that scans the document and reads the data from the marked fields. 

1. OCR:

Optical Character Recognition (OCR) is an input device that is used to scan the printed/ handwritten text materials into computer-readable text making it easy to edit and store. It is used to read the cheque numbers in the banks arid millions of magazines and letters are sorted every day by OCR machines.

2. MICR:

Magnetic Ink Character Reader enables special characters printed in magnetic ink to be read and input rapidly to a computer. MICR is used extensively in banking because magnetic- ink characters are difficult to forge and are therefore ideal for marking and identifying cheques.

The mouse is an input device used to point to a particular place on the screen and select it in order to perform one or more actions. It can be used to select menu commands, size windows, start programs, etc. The most common kind of mouse has left and right buttons on top. The left mouse button is normally used to select the items on the screen. The different types of are mechanical mouse, optomechanical mouse, and optical mouse.

The set of tracks of a hard disk drive which can be accessed without changing the position of the access arm is called cylinder.

A magnetic tape is a data storage device which has oxide coating on a plastic strip. The tape can retain electronically encrypted data that can range from voice to audio to data information.

The head of the hard disk is used to read and write data.

RAM (random access memory) is a primary memory in a computer where the operating system, application programs, and data currently in use are kept so that they can be quickly accessed by the CPU. RAM is much faster to read from and write to than the other kinds of storage in a computer. It is a volatile memory which that means data can be stored ones as long as the computer is on. There are different types of RAM.

1. Static RAM:
SRAM is one type of RAM and it is a volatile memory. In an SRAM, each bit that stores data is made up of four or six transistors that make up a flip-flop. There are additional transistors that are used to control read and write accesses of storage cells. Each SRAM cell can be in three different states called to read, write and standby. A cell is in the reading state when data has been requested and it is in writing state when the data in the cell is modified. The cell is in the standby state when it is idling.

2. Dynamic RAM:
DRAM is also a volatile memory that uses separate capacitors to store each bit. Capacitors, when not charged, represent the value 0 of a bit and when charged represent the value 1. Since the capacitors discharge with time, they need to be refreshed periodically to maintain the values stored in them. Each memory cell in a DRAM consists of a capacitor and a transistor and these cells are arranged in a square array.

3. SDRAM Synchronous Dynamic Random Access Memory:
SDRAM is a type of main memory that synchronizes itself with the computer’s system clock. This type of memory synchronizes its input and output signals with the incoming clock that is used in the system board. Its speed rating is given in MHz to easily compare it to system board bus speeds.

By doing so, data transactions can continually take place with each successive rising edge of the clock. The clock is used as the main determining factor for memory data operation. The memory array is composed of two banks that can be accessed independently.

4. EDO RAM:
EDO is short for Extended Data Out-and is a type of memory that was first used with Pentium computers. EDO allows a CPU to access memory 10 to 15 percent faster than the compatible Fast Page memory.

5. DDR RAM:
DDR (Double Data Rate DRAM) is similar to SDRAM. The transfer of data for DDR components can be performed at both edges of the clock signal. This allows a double rate of transmission speed enabling the device to operate at speeds twice that of typical SDRAM devices.

6. DDR2 RAM:
The main benefit is speed runs its bus at twice the speed of the memory cells it contains. This enables faster bus speeds than older DDR memory. It also consumes less power than DDR.

The rotational speed is 7200 revolutions per minute.

A hard disk is a secondary storage device. It consists of several metal platters/plates coated with a magnetic material.

Line printers are high-speed printers capable of printing an entire line at a single strike. A fast line printer can print as many as 3,000 lines per minute. The disadvantages of line printers are that they cannot print graphics, the print quality is low, and they are very noisy.

The Magnetic Tapes is the Type of Secondary Storage device and is used for taking backup of data. They contain some magnetic fields and are used to convert data into sequential form and load into the tape. They contain a ribbon which is coated with the magnetic material only on one side. There is ahead which accesses and reads the data which is recorded on the tape. While accessing/reading data it is possible to move along to different locations either forward. On backward to get the required information. The only hitch is one cannot directly land on a location, but has to wind forward on rewind as the case may be to get to the required data. Tape drives are used for inserting and winding/new winding to tapes mag. Tapes are prone to get damaged easily due to human errors. A very large amount of data can be stored, in the tap.

Advantages:

• The cheapest form of storage per megabyte of storage.
• Can store large amounts of data in terabytes per tape cartridge.
• It can be used to do the back up overnight or over the weekend.

Disadvantages:

• Slow due to serial access technique
• Need a special piece of equipment to record and read the data.
• The data may get corrupted if the tape is placed near a strong magnetic field.

It is a text base input device that allows the user to input alphabets, numbers and other characters. It consists of a set of keys mounted on a board.

The different keys are as follows:

1. Alphanumeric Keypad:

It consists of keys for the English alphabets, 0 to 9 numbers, and special characters like + “ / * ( ), etc.

2. Function Keys:

There are twelve function keys labeled F1, F2, F3… F12. The functions assigned to these keys differ from one software package to another. These keys are also user-programmable keys

3. Special-function Keys:

These keys have special functions assigned to them and can be used only for those specific purposes. The functions of some of the important keys are defined below.

(i) Enter:

It is similar to the ‘return’ key of the typewriter and is used to execute a command or program.

(ii) Spacebar:

It is used to enter a space at the current cursor location.

(iii) Backspace:

This key is used to move the cursor one position to the left and also delete the character in that position.

(iv) Delete:

It is used to delete the character at the cursor position.

(v) Insert:

Insert key is used to toggle between insert and overwrite mode during data entry.

(vi) Shift:

This key is used to type capital letters when pressed along with an alphabet key. Also used to type the special characters located on the upper side of a key that has two characters defined on the same key.

(vii) Caps Lock:

Caps Lock is used to toggle between the capital lock features. When ‘on’, it locks the alphanumeric keypad for capital letters input only.

(viii) Tab: 

Tab is used to move the cursor to the next tab position defined in the document. Also, it is used to insert indentation into a document.

(ix) Ctrl: 

The control key is used in conjunction with other keys to provide additional functionality on the keyboard.

(x) Alt:

Also, like the control key, the Alt key is always used in combination with other keys to perform specific tasks. 

(xi) Esc:

This key is usually used to negate a command. Also used to cancel or abort executing programs.

4. Numeric Keypad:

Numeric keypad is located on.the right side of the keyboard and consists of keys having numbers (0 to 9) and mathematical operators (+ “ * /) defined on them. This keypad is provided to support quick entry for numerical data.

5. Cursor Movement Keys: 

These are arrow keys and are used to move the cursor in the direction as indicated by the arrow (up, down, left, right).

1. CD ROM:

Compact disks are known as optical storage devices. A compact disc is a thin, circular disc of metal and plastic about 12cm (just over 4!4 inches) in diameter. It’s actually made up of three layers. Most of a CD is made from a tough, brittle plastic called polycarbonate. Sandwiched in the middle there is a thin layer of aluminum. Finally, on top of the aluminum, is a protective layer of lacquer. There is a shiny side and dull side. The dull side usually has a label on it telling you what’s on the CD; the shiny side is the important part. It’s shiny so that a laser beam can bounce off the disc and read the information stored on it.

A CD can store around 650 MB of data. It comes in two main forms namely CD-ROM CD Read-Only memory in which data can only be written once and CD-RW CD ReWriteable means data new can be saved on the disk over and over again.

2. Digital Versatile Disk (DVD):

A DVD is similar to a CD in that it is an optical device and that a laser is used to store and read the data. A single layer DVD can store about 4.7GB of data and a double-layer DVD can hold over 9 GB data. DVDs do not work on CD drives but DVD drives can read CDs. There is no single standard of DVD. They can be easily damaged by breaking or scratching.

3. Blu ray dies: 

The Blu-ray is an optical storage unit and its technology is identical to CDs and DVDs. But the difference is a blue laser is used in Blu-ray disc instead of the red lasers that were used in the earlier versions. The BluRay standard was established to hold a standard-length movie in HDTV format, or high-definition television. Such movies are displayed in significantly higher resolution and therefore they require much more storage space.

A standard Blu-ray disc holds 27GB (gigabytes) of information which is about 40 times the amount of data that a CD can hold. Blue lasers have a shorter wavelength (450 nano meters) than red lasers (650 nano meters), and therefore the beam can be focused on a smaller area which means that more data can be packed on an identically sized disc.

The keyboard is a standard input device. It is used to input data and programs to the computer. It has alphabets, numeric and symbol keys. It has special keys including function keys, control keys, and arrow keys. Today most users use the QWERTY style keyboards. Keyboards are connected to the computer through cables or wireless. The ergonomic keyboard, virtual keyboard, and compact keyboard are a few other special types of keyboards.

Hard disk is a secondary storage device. It is a disk pack consisting of several metal platters coated with a magnetic material, rotating at high speed (7200 revolutions per second). Each surface has a read/write head mounted on an arm. The heads can only move in one radial direction. Both sides of a platter are used. Each surface is divided into concentric circles or tracks, typically 1000 tracks per platter.

Each track is divided into about 100 sectors, separated by gaps. To access data in a specific location, the arm has to be positioned over the proper track, this takes about 10-20 ms (1 ms = 1 millisecond = 0.001 s). The head waits until the desired sector is under it; this takes about 6 ms. Once the sector is found, the data can be read at a rate of 4 Mb/s.
Hard Disk Components:
A number of disks on which data is stored (the more disks, the greater the drive’s capacity).

• A motor to rotate the disks
• Ahead to read and write data (The heads “fly” over the surface of a disk supported by a few molecules of air)
• An actuator to move the heads over the disks

Each disk is segmented radially into tracks. Tracks are about 300 millionths of an inch apart. Each track is divided into sectors. A sector is the smallest addressable unit on a direct access storage device.

A cylinder is made up of all the tracks that are at the same location of each platter in the device.
The storage capacity of the hard disk ranging from several GigaBytes (250GB) to several Terra Bytes (2 TB). There are internal hard disk and external hard disks.

The arrangement of tracks and sectors on a disk is known as its ‘format’.

Data is stored on the surface of a platter in sectors and tracks.

Ink-jet printers are non-impact line printers. The ink is stored in disposable ink cartridges, often a separate cartridge is used for each of the major colors. It prints by spraying small, electrically charged droplets of ink from nozzles through holes in a matrix at high speed onto paper. Ink-jet printers can print in color and are noiseless and cheaper than a color laser printer. However, they are slower and the print resolution is between 300 and -1200 dpi.

The laser printer uses a laser to draw the image onto the printer’s drum, which carries an electric charge. The parts of the drum hold the electrical charge are able to pick up the dry powder type of ink, also called toner, from within the printer. This ink is then fused to the paper, using heat, as the paper rolls over the drum. After the document is printed, the electrical charge is removed from the drum and the excess toner is collected. Laser printers produce good quality prints with resolutions ranging from 300 dpi to 1200 dpi.