Computer Peripheral Devices | Computer Science for Class 7 PDF Download

Peripheral Devices

A computer peripheral is any external device that provides input and output for the computer. For example, a keyboard and mouse are input peripherals, while a monitor and printer are output peripherals. Computer peripherals, or peripheral devices, are sometimes called “I/O devices” because they provide input and output for the computer. Some peripherals, such as external hard drives, provide both input and output for the computer.

• Memory or storage: It saves program instructions and data.
• Input devices: Input devices allows user to communicate with computer by accepting data.
• Output devices: Output devices enable the computer to present information to user.

The input and output devices are collectively known as peripheral devices.

Input devices

Keyboard

• Standard keyboard has 104 keys
• The most commonly used keyboard is called QWERTY Keyboard.
• Toggle Keys – A toggle key toggles the input from a group of keys on a keyboard between two different input modes. The most common toggle key is Caps Lock, which toggles the letter keys between lowercase and uppercase mode. Other toggle keys are Num Lock, Scroll Lock, and Insert.
• Modifier keys – a special key (or combination) that temporarily modifies the normal action of another key when pressed together
  For example, Shift + A gives Capital A and Alt + F4 will close the program in the active window.
• Special keys – function keys, control keys, arrow keys, and so on.
• Punctuation keys – comma, period, semicolon, and so on.
• Alphanumeric keys – letters and numbers
• The keys on computer keyboards are classified into three categories.
• The most common input device is Keyboard. It is similar to type writer and also contain additional keys.

(i) Special Purpose Key

Tab key

• In word processing pressing tab key will mouse the cursor to the next tab stop.
• In spread sheet pressing tab key move the cursor to the next cell.
• When filling an online form, pressing tab key move cursor to next field.
• Shift + Tab will mouse the cursor to the previous field.
• It eliminate the use of mouse to click in and adjacent field.

Caps Lock Key

• It is on the left side of the keyboard.
• It is a toggle key which toggle key between lower case and upper case every time it is pressed

Caps Lock and Num Lock are known as toggle keys

Space bar key

• It is the longest key on the keyboard.
• It is use to create space between the two word.

Enter Key

• It is used to move the cursor to the beginning of the next line to complete the paragraph.
• It is also called as Return Key.

Backspace Key

• It is used to delete the character just to the left of the cursor and moves the cursor to that position.

Delete Key:

• Sometimes labelled as Del.
• It deletes the character which are on the right side of the cursor and does not mouse the cursor.
• It also deletes the selected text.

Esc Key

• It is used to exist from program, like in power point presentation, the slide show is exist by pressing escape key.

Prt Scr ( Print Screen )

• When we press this key it either send the image of display to the printer or to the computer clip board depending on the OS.

Pause ( Break Key )

• It is used to temporality pause the action of a application program.

Home Key

• It is used to move the cursor to the beginning of the work area like to move cursor to the beginning of sentence.

End Key

• It is used to move the cursor to the end of the work area.

Page up

• It is used to display the previous page of a document.

Page down

• It is used to view the next page of a document.

Mouse

A Mouse is a device that controls the movement of the cursor or pointer on a display screen, i.e. a monitor. Its name is derived from its shape, which looks a bit like a mouse, its connecting wire that one can imagine to be the mouse’s tail.
Mouse was invented by Douglas Engelbart of Stanford Research Center in 1963.

There are three types of Mouse. They are,
(i) Mechanical Mouse: It has a rubber or metal ball on its underside that can roll in all directions.

(ii) Optical Mouse: Uses a laser to detect the mouse’s movement. Optical mouse have no mechanical moving parts. They respond more quickly and precisely than mechanical mouse.

(iii) Cordless Mouse: Usually called as Bluetooth Mouse. These kind of Mouses are not physically connected at all. Instead they rely on infrared or radio waves to communicate with the computer. They are bit expensive.

Way of operation the mouse
(i) Single click

• When the left button of the mouse is clicked (pressed) once it selects the item on which the cursor was pointing.
• If you perform single click when the cursor is on a file or folder, it gets selected and we come to know because the selected file or folder turns blue.

(ii) Double Clicks

• When the left button of the mouse is clicked twice with a short interval, it opens the file or folder on which the cursor was pointing.
• In word, to select a single particular word we use double click.

(iii) Right Click

• When the Right button of the mouse is clicked, it displays a list of commands on the screen.

(iv) Drag and Drop:

• When icon is pointed by the cursor on the screen and if we press the left button of mouse and move the cursor to other location and then release the button then the icon is moved to the new location on the screen. This is called Drag and Drop.
• To select some text we drag the mouse cursor over the text we want to select.

Joystick

Joystick was mainly used for Gaming purposes and also for CAD/CAM systems. It has a lever that moves in all directions and controls the movement of a pointer or some other display symbol. Nowadays Joystick has become an old thing and different types of Game Controllers replaced it gradually.

Scanner

Scanner is a device used to convert an image of photographic prints, posters, or magazine pages into it’s digital form. High resolution scanners are used for scanning for high-resolution printing, but lower resolution scanners are adequate for capturing images for computer display. Scanners are attached to the CPU and the scanned image will be displayed on the monitor. Scanners usually come with software, such as Adobe’s Photoshop product, that makes the user to re-size and modify the captured image.

Microphone

It is a device used to input the Sound. It is usually called as mic and in most of the Laptops, Mic comes in-built. Microphone is also used to enter text with voice recognition software.

Bar Code Reader

A bar code reader, also called a price scanner, is a simple hand-held input device used to capture and read information contained in a bar code. Most of the super-markets, big jewelry shops, cloth shops, etc use this Bar code Reader. It consists of a scanner, a decoder, and a cable used to connect the reader with a computer. The bar code reader simply captures and translates the bar code into numbers and/or letters, the data must be sent to a computer so that a software application can make sense of the data.

OCR (Optical Character Recognition)

OCR devices are capable of reading data that are in typed or hand- written form. It is a combination of a scanner and a software, that converts the printed data into ASCII. It is widely used as a form of data entry from printed paper data records, whether passport documents, invoices, bank statement, receipts, business card, mail, or other documents. OCR is a field of research in pattern recognition, artificial intelligence and computer vision.

OMR (Optical Mark Recognition)
OMR is a device which senses the presence or absence of a mark. It is also known as Mark Sensing. In competive exams like UPSC, SSC and other state level public service examinations, the candidates are provided with the OMR sheet and asked to mark it. The OMR device evaluated the OMR sheets accurately and also it reduces the time to a great extent. Just imagine how much time it will take to evaluate more than 15 lakhs of OMR sheets manually.

MICR (Magnetic Ink Character Recognition)

Magnetic Ink Character Recognition is a character recognition system that uses special ink and characters. It is a character-recognition technology used mainly by the banking industry to ease the processing and clearance of cheques and other documents. The MICR encoding, called the MICR line, is at the bottom of cheques and other vouchers and typically includes the document- type indicator, bank code, bank account number, cheque number, cheque amount, and a control indicator. MICR provides a secure, high-speed method of scanning and processing information.

Web Camera

Web Camera is a device which is used to view image in real time. It is mostly useful in video-calling with softwares such as Skype and also used in Video-conferencing in MNCs, and also as security cameras.

Output devices

Output is a processed data that is otherwise called information. Output Devices or Output Units do not compute or process anything. Those devices just display the results in hard copy or soft copy.
The commonly used Output Devices are,
Monitor
A monitor is an electronic visual display for computers. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD) thin panel, while older monitors used a cathode ray tube (CRT) about as deep as the screen size. The Organic light-emitting diode (OLED) monitors provide higher contrast and better viewing angles than LCDs but they require more power when displaying documents with white or bright backgrounds.

Types of monitors

• Cathode Ray Tube (CRT): This monitor uses a Cathode Ray Tube (CRT). CRT tube creates an image on the screen using a beam of electrons. CRT consists of one or more guns that fire a beam of electrons inside the screen. The screen is coated with very tiny Phosphor dots from inside. The beam of electrons repeatedly falls on the surface of screen. Every beam fall takes only a fraction of second. CRT in color monitors consists of three guns.
• Flat Panel Monitors: Flat Panel Monitors take less space and are lightweight. These monitors use much less power than CRTs. It does not emit harmful radiations. It is much expensive than CRT. Notebook computers, PDA and cellular phones use flat panel monitors. Flat panel monitors are available indifferent sizes such as 15”, 17”, 18” & 19” etc.
• Liquid Crystal Display: Liquid crystal display screen contains a substance called liquid crystal. The molecules of this substance line up in such a way that the light behind the screens blocked or allowed to create an image. LCDs provide a sharper picture than CRTs and emit less radiation. LCD displays requires less power and take up less space than CRT.
• Gas plasma Display: Gas plasma display uses gas plasma technology. This technology uses a layer of gas between two glass plates. The gas release ultraviolet light when voltage is applied. The pixels on the screen glow due to this ultraviolet light and form an image. Plasma display is available in the sizes of upto 150 inches wide.

Types of touch Screen Monitors

There are different types of touch screen technology. The most common types are Resistive, Surface wave & Capacitive.

• Resistive Touch Screen: This monitor usually has a coat of thin electrically conductive and resistive layer of metal. A change in electrical current occurs when it is pressed. The input can be processed by a computer. These monitors are the most popular types of touch screen monitors used today. They are usually not affected by dust or liquids which make them very reliable.
• Surface Wave Touch Screens: These monitors use ultrasonic waves to process input from the screen. These waves flow over the touch screen. The wave is absorbed and processed by computer when a person touches the pad.
• Capacitive Touch Screen: These screens are coated with indium tin oxide. This material provides continuous current across the screen. The current can be measure by the processor when the pad is touched. It is usually used with a bare finger instead of stylus. These screens have high clarity and are not affected by dust. Nowadays most of the smart phones have Capacitive Touch screens.

Projector
It is a device used to project an image on the flat surface like computer screen. It is mainly used in presentations, seminars, and meetings. They are also used in schools. Home theater enthusiasts also use them as a good projector will display an image that looks better and more accurately represents the source material than most TVs on the market ever would.

Printer
Printer is a device that is capable of printing the processed data from the computer. It can print document or an image.

Different Types of Printers

• Inkjet printers, also sometimes called bubble jet printers use colored ink they put on a paper.
• Dye sublimation printers produce very high quality images. Three colors are used – Cyan, Magenta and Yellow.
• Dot-matrix printers are now almost extinct. They used a ribbon and made a lot of noise.
• Daisy Wheel printers are a typewriter printer; Results look hand-typed with excellent looking text, no real graphics and very loud.
• Laser printers transfer tiny particles of toner onto the paper.

Speaker
Speaker is a hardware device that is connected to a computer’s sound card. The sound card outputs the sound generated by the computer.

Plotter
Plotter is a device that draws pictures on paper based on commands from a computer. Plotters differ from printers in that they draw lines using a pen. Multi-color plotters use different-colored pens to draw different colors. Plotters are considerably more expensive than printers. They are used in engineering applications where precision is mandatory.