Kerala Plus One Computer Science Notes Chapter 3 Components of the Computer System
Computer is a electronic device that can perform variety of operations.
Hardware is the tangible and visible parts of a computer, which consists of some electromechanical components. These hardware components are associated with the functional units of a computer.
A processor is responsible for all computing and decision making operations and coordinates the working of a computer. The performance of a CPU determines the overall performance of the computer. The CPU is an Integrated Circuit (IC) package is also microprocessor, eg., Intel core 13, core 15, core 17, AMD Quadcore.
These are storage locations inside CPU, whose content can be accessed more quickly by the CPU than other memory. They are temporary storage areas for instructions or data. They are not a part of memory. They are special additional storage locations. It speeds up the execution of programs. Registers are divided into:
- Accumulator: It is a part of the arithmetic Logic Unit (ALU). This register is used to store data to perform arithmetic and logical operation. The result of an operation is stored in the accumulator.
- Memory Address Register (MAR) : It stores the address of a memory location to which data is either to be read or written by the processor.
- Instruction Register (IR): The instructions to be executed by the processor are stored in the instruction register.
- Program Counter (PC): It holds the address of the next instruction to be executed by the processor.
It is a large Printed Circuit Board (PCB) to which all the major components including the processor are integrated. It also provides expansion slots. The motherboard must be compatible with the processor chosen.
These are devices that are attached to a computer system to enhance its capabilities.
Ports are used to connect external devices. Peripherals include input devices, output devices, external storage and communication devices. Different ports are:
1. Serial port:
Also called serial communication port which transmits data one bit at a time. Serial cables are cheaper to make and easier to shield from interference. Since its speed is too low, they are being replaced by faster ports like PS/2, USB, etc.
2. Parallel ports:
It can transmit several bits of data simultaneously. It is faster than serial port and is used to connect a printer or scanner to the computer.
3. USB (Universal Serial Bus):
It is a connection that provides high speed data communication between devices. Due to its high bandwidth data transfer is faster it is used for short distance communication.
Main advantages of USB are:
- USB ports are capable of supplying electric power to external devices.
- USB devices can be connected and disconnected even when the power is on.
4. LAN port:
Also referred to as an Ethernet port. It allows a computer to connect to a network using a wired connector like jack RJ45
5. Personal system /2 (PS/2) ports:
These are special ports invented for connecting the keyboard and mouse. These types of ports are too slow and replaced by faster ports like USB now a days.
6. Audio ports:
These are used to connect audio devices like speakers, microphone, etc. Audio ports are divided into line in, line out, mic in.
7. VGA (Video Graphics Array):
It is a port is used to connect a monitor or a projector to a computer.
8. HDMI (High Definition Multimedia Interface):
It is a type of digital connection capable of transmitting high-definition video and multichannel audio over a single cable/refer.
It is a place where we can store data, instructions and results temporarily or permanently. Memory can be classified into two:
1. Primary memory:
Also refers to the main memory. It holds data, intermediate results and results of on-going jobs temporarily. This includes mainly three types of memory. They are:
i. RAM (Random Access Memory):
The microprocessor can read from and write to. Data can be stored and retrieved at random from anywhere within the RAM, no matter where the data is. The contents of RAM are lost when power is switched off. Therefore, RAM is a volatile memory. The speed of a RAM refers to how fast the data in memory is accessed and expressed in Mega Hertz (MHz). The contents of RAM are:
- The operating system software.
- The application software currently being used.
- Any data that is being processed.
ii. ROM (Read Only Memory):
It can perform only read operations and its contents cannot be easily altered. ROM is nonvolatile; the contents are retained even after the power is switched off. It is used to hold boot up program known as Basic Input Output System (BIOS). This software runs when the computer is switched on or ‘boots up’. It checks the computer’s hardware and then loads the operating system. ROM is slower than RAM.
Different types of ROM are:
- PROM (Programmable ROM) which can be programmed only once, ie., at the time of manufacture.
- EPROM (Erasable Programmable ROM) that can be erased using ultra violet radiation.
- EEPROM (Electrically Erasable Programmable ROM) which can be erased and rewritten electrically.
iii. Cache memory:
It is a small and fast memory between the processor and RAM. Frequently accessed data, instructions, intermediate results, etc. are stored in cache memory for quick access. Cache is more expensive than RAM.
2. Secondary memory:
Also known as auxiliary memory. It holds data and information permanently. The data stored in it does not vanish when power is turned off. Secondary memory is much larger in size than RAM, but is slower. It stores programs and data but the processor cannot access them directly. It is also used for transferring data or programs from one computer to another. It also acts as a backup.
Various devices in this type are:
i. Magnetic storage device:
It uses plastic tape or metal plastic discs coated with magnetic materials. These are:
- Magnetic tape: It is a backup device that can store huge volume of data. The cost per unit volume of a magnetic tape is less compared to other magnetic storage devices. It is a recording medium consisting of a thin tape with a coating of fine magnetic material. It can be used for recording analogue or digital data. Data is stored in frames across the width of the tape with a read/ write head.
- Hard disk: It consists of metal disks coated with magnetic material concealed in dust free containers. Hard disks have very high storage capacity, high data transfer rates and low access time. It is more durable and less error prone. Each platter requires two read/write heads, one for each surface. A tiny electromagnetic read/write head attached to an access arm magnetises tiny spots on the disk to store data. The same electromagnetic head can later sense the magnetic fields of the spots, allowing the data to be read back from these disk.
ii. Optical storage device:
Optical disk: It is a data storage medium which uses low-powered laser beam to read from and write data into it. It consists of an aluminium foil sandwiched between two circular plastic disks. The main types of optical disks are:
a. Compact Disc (CD) is an optical storage medium capable of storing upto 700 MB of data. A CD drive uses red laser beams for reading from and writing data into CD. Two types of CDs are CD-R (recordable) and CD- RW (Re-writable).
b. Digital Versatile Disk (DVD) higher storage capacity is achieved by using smaller spots to record data. Recording and reading of data is done using DVD drive. The capacity of a DVD varies from 4.37 GB to 15.9 GB. There are three major types of DVDs: DVD-ROM, DVD-RW and DVD-RAM.
A normal DVD known as DVD-5 stores 4.37 GB data where as a dual layer double side DVD known as DVD-18 can store 15.9 GB.
c. Bluray DVD is used for recording, rewriting and playback of High Definition (HD) video as well as storing huge amounts of data. Bluray format uses a blue-violet laser. So it has the name Bluray. The benefit of using a blue-violet laser is that it has a shorter wavelength which makes it possible to focus the laser spot with greater precision. This allows data to be packed more tightly. Therefore it is possible to store more data on the disk. Can hold up to 25 GB on a single layer disc and 50 GB on a dual-layer dise.
iii. Semiconductor memory:
Also known as flash memory. Flash drives use the EEPROM chips for data storage. Flash memory is faster and durable when compared to other types of secondary memory.
Various types of flash memories are:
- USB flash drive: It is a small external storage device which consists of flash memory. These are portable and rewritable.
- Flash memory cards: Flash memory cards have a smaller version which is used within cell phones, tablets, etc.
Input/ output device
These are required for users to communicate with the computer. Since they reside outside the CPU,they are called peripherals.
It is used to feed data into a computer. It is defined as a device that provides communication between the user and the computer. Different input devices are:
It is the most common input device. It allows the user to input alphabets, numbers and other characters. Keyboard detects the key pressed and generates the corresponding ASCII code which can be recognised by the computer. It has a keyboard layout called the QWERTY design.
Keyboards can be classified as:
- Wired keyboards are connected to the CPU through a serial, PS/2 port or USB port.
- Wireless keyboards are connects to the computer through infrared, radio frequency or Bluetooth connections.
It is a small hand-held device used to indicate the position of a cursor or its movement on a computer display screen by rolling it over a mouse pad/flat surface. A mouse has one or more buttons and possibly a scroll wheel. Scroll wheel is used for scrolling the screen vertically or horizontally.
The different types of mouse:
- Ball optical works on the principle of the movement of the ball.
- Laser mouse use laser beams for sensing movement. Laser mouses are wired and wireless.
It is a pointing device shaped like a pen. The tip of the lightpen contains a light-sensitive element which when placed against the screen enabling the computer to identify the location of the pen on the screen. The advantage is drawing directly on to the screen.
4. Touch screen:
It allows the user to operate by simply touching on the display screen. It can also be operated using a stylus which gives more precision.
5. Graphic tablet:
It consists of an electronic writing area and a special “pen” that works with it. Also allows artists to create graphical images with motions and actions similar to traditional drawing tools. The pen of the graphics tablet is pressure sensitive.
It is a pointing device found on the portable computers and some external keyboards. Touchpad is operated by using finger and dragging it across the flat surface.
It is used for playing video games, controlling training simulators and robots. The joystick has a vertical stick which can move in any direction. It has button on the top that is used to select the option pointed by the cursor.
It can be attached to a computer to input sound. It accepts sound which is analogue in nature as input and converts it to digital format.
It can capture information, like pictures or text, and convert it into a digital format that can be edited using a computer. The quality of the image depends on the resolution of the scanner. The resolution of the image scanned is expressed in Dots Per Inch (DPI). The higher the DPI, the better the resolution. The different variance of scanners are:
- Flat bed can scan from a book.
- Sheet feed can scan a single sheet.
- Hand held scanner is portable.
10. Optical Mark Reader (OMR):
It scans a printed form and reads predefined positions, and records the marks on the form. It is useful for applications in which large number of hand-filled forms needs to be processed quickly with great accuracy.
11. Barcode readers:
These are devices that are used to input data from such set of barcodes. A QR (Quick Response) code is similar to barcodes. Barcodes are single dimensional whereas QR codes are two dimensional. The two dimensional way of storing data allows QR code to store more data than a standard barcode.
12. Biometric sensor:
It is a device that identifies unique human physical features with high accuracy. Biometric system uses physical features like fingerprints, retina, iris patterns, etc., to identity of the user. The three major types of biometric sensors; semiconductor sensor, optical sensor and ultrasound sensor.
13. Smart card:
It is a plastic card that stores and transacts data. The data card may contain memory or a microprocessor. Smart card readers are used to access data in a smart card. It can be contact type or contactless.
14. Digital camera:
It can take pictures and videos and convert them into digital format are stored inside its memory and can be transferred to a computer by connecting the camera to it.
The quality of the picture is determined by the number of pixels in each picture. Digital cameras have resolutions ranging from 2 megapixel to 24 megapixels. Web camera is a compact and less expensive version of a digital camera.
These devices that print/ display output from a computer. Outputs generated by the output device
- Hardcopy outputs are permanent outputs which can be used at a later date or when required.
- Softcopy outputs are electronic and are available on the screen in a digital form.
1. Visual Display Unit (VDU):
It visually conveys text, graphics and video in-formation. Information shown on a display device is called softcopy because the information exists electronically and is displayed for a temporary period of time.
The pixel spacing on the screen is called the dot pitch. A screen with smaller dot pitch produces sharper images. Response time refers to the time taken for a pixel to turn from a state of darkness and then back again. Display devices are:
i. Cathode Ray Tube (CRT) monitors:
It resembles television sets of the past. Two types CRT monitors are:
- Monochrome monitor displays characters and images in a single colour on a dark background.
- Colour monitor uses three different basic colours such as red, blue and green.
ii. Liquid Crystal Display (LCD) monitors:
LCD displays consists of liquid crystal sandwiched between two plastic plates. These crystal rearrange to from an image when an electric current is passed through them. A light source at the back of this plate makes the picture visible. This light source can be fluorescent lamp or LED.
iii. Light Emitting Diode (LED) monitors:
It use LED directly behind the liquid crystal display (LCD) in order to light up the screen. This technique is very effective and gives each area of the screen its own light, which can be on or off. This technology is expensive. The advantage of using LED is better color quality, clarity, wider viewing angle, faster refresh rates and power savings.
iv. Plasma monitors:
A flat- panel display consists of sandwiching neon/xenon gas between two sealed glass plates with parallel electrodes deposited on their surfaces. When a voltage pulse is passed between two electrodes, the gas lights up as different colours, creating images on a monitor. Plasma monitors provide high resolution but are expensive.
v. Organic Light Emitting Diode (OLED) Monitors:
The panel of OLED is made up of millions of tiny LEDs. The O stands for Organic, which means there is carbon in the light emitting layer of the panel. OLED screens are thinner and lighter than LCDs and LEDs. OLEDs consume less power, but are very expensive.
vi. LCD projector:
It is a type of video projector for displaying video, images or computer data on a large screen or other flat surface. Beam of light then passes through a lens which projects and focuses the image on the surface.
These are used to produce hardcopy output. Based on the technology used, they can be classified as:
i. Impact printers:
It uses the typewriting or printing mechanism where a hammer strikes the paper through a ribbon in order to produce output. eg., Dot-matrix printers use small electromagnetically activated pins in the print head and an inked ribbon, to produce images by impact. These printers are slow and noisy.
ii. Non-impact printers:
They do not touch the paper while printing. They use different technologies to print characters on paper. Two factors that determine the quality of a printer are its resolution and speed.
Categories of this printers are:
- Inker printers form the image on the page by spraying tiny droplets of ink from the printed head. The printer needs several colour of ink. These are inexpensive, but the cost of ink cartridge makes it a costly.
- Laser printer produces good quality output. The image to be printed is transferred to a drum using a laser beam. The toner powder from the toner cartridge is then sprayed on the drum. The toner powder sticks onto the portions traced the drum by the laser beam. It is transferred to a paper rolling the paper on the drum. Through heating the powder is fused on to the paper. Laser printers are faster and their speed is in page per minute (ppm).
- Thermal printer produces a printed images by selectively heating heat-sensitive thermal paper when it passes over the thermal print head.
It is an output device used to produce hard copies of graphs and designs on the paper. These are of two types:
- Drum plotter: Also known as roller plotter. It consists of a drum or roller on which a paper is placed and the drum rotates back and forth to produce the graph on the paper. The drawing arm moves side to side as the paper is rolled back and forth through the roller.
- Flatbed plotter: Also known as table plotter. It plots on paper that is spread and fixed over a rectangular flatbed table. They uses two drawing arms, each of which holds a set of coloured ink pens or pencils. The drawing arms move over the stationary paper and draw the graph on the paper. It is very slow in drawing or printing graphs.
4. 3D printer:
It is a new generation output device used to print 3D objects. The 3D printing process turns the object to be printed into thousands of horizontal tiny little layer. These tiny layers stick together to from an solid object.
It produces sound. The speaker produce sound by the movement of the diaphragm in the speaker forward and backward according to the electrical signals coming out of the audio port.
Electronic waste (e-Waste)
It is defined as discarded computers, office electronic equipment, entertainment device, mobile phones, television sets and refrigerators. This global mountain of waste is expected to continue growing at 8% per year. There are different e-waste disposal methods:
- Reuse: It refers to second-hand use or usage after the equipment has been upgraded or modified. This method reduces the volume of e-waste generation.
- Incineration: It is a controlled and complete combustion process in which the waste is burned in specially designed incinerators at a high temperature in the range of 900 to 1000 degree Celsius.
- Recycling: It is the process of making or manufacturing new products from a product that has originally served its purpose.
- Land filling: The most widely used but not recommended methods for disposal of e- waste. In this method soil is excavated from the trenches made and waste material is buried in it, which is covered by a thick layer of soil.
It is the study and practice of environmentally sustainable computing or IT. To pro-mote green computing, there are 4 approaches are used. They are:
- Green design: Designing energy efficient and ecofriendly computers and devices.
- Green manufacturing: Minimising waste during the manufacturing of IT devices.
- Green use: Minimising the electricity consumption of computers.
- Green disposal: Reconstructing used computers or appropriately disposing off or recycling unwanted electronic equipment.
Software is a general term used to denote a set of programs that help us to use computer system and other electronic devices efficiently and effectively. The two types of soft-wares are:
1. System software:
It is a set of one or more programs designed to control the operations of a computer. It supports the running of other software, its communication with other peripheral devices. It helps the user to use computer in an effective manner. The following are components of system software:
i. Operating system:
It is a set of programs that acts as an interface between the user and computer hardware. The primary objective of an operating system is to make computer system convenient to use. Operating system is the most important system
Main functions of operating system are:
- Process management.
- Memory management.
- File management.
- Device management.
ii. Language processors:
The instructions to the computer are written in different languages. They are:
- High level languages: The instructions are written in English which are simple and can be easily understood, eg., C, C++, COBOL, VB, Java etc.
- Low level languages: These are machine oriented languages and are written using the memory and registers. There are two types of low level languages:
Machine languages are represented by using os and is. It is very difficult to write these types of languages.
Assembly languages use mnemonic symbols like ADD. It is very easy compared to machine language.
Various language processors are:
- Assembler: It converts languages written in assembly language into machine language.
- Interpreter: It converts a high level language into machine language by line by line. If there is an error in one line, it reports and the execution is terminated. It will continue the translation only after the correction of the error, eg., BASIC is an interpreted language.
- Compiler: It translate a high level language into machine language by converting all the lines at a time. The errors are provided at the end of the compilation. The programming language that have a compiler are C, C++, Pascal, etc.
iii. Utility software:
A set of programs which help users in system maintenance tasks and in performing tasks of routine nature. Utility programs are:
- Compression tools: Large files can be compressed so that they take less storage area. Compression of files is known as zipping and decompression is called unzip-ping, eg., WinZip, WinRAR.
- Disk defragmenter: It is a program that rearranges files on a computer hard disk. This enables the computer to work faster and more efficiently.
- Backup software: It duplicating the disk information so that in an event of disk failure or in an event of accidental deletion, this backup may be used. Backup utility programs facilitates the backing up of disk.
2. Application software:
It is the software developed for specific application. It includes:
i. General purpose software:
These are used to perform operations in a particular application area. General purpose software is classifieds as:
- Word Processing software is designed for creating and modifying documents, eg., MS Word, Open Office Writer, etc.
- Spreadsheet software allows users to perform calculations using spreadsheets, eg., Microsoft excel, Open Office calc, Lotus 1-2-3 and Apple numbers.
- Presentation software is used to display information in the form of a slide show, eg., Microsoft Power Point, Open Office Impress.
- Database is an organised collection of data arranged in tabular form. Database Management System (DBMS) consists of a collection of interrelated data and set of programs to access those data, eg., Microsoft Access, Oracle, PostgreSQL, My SQL, etc.
- Multimedia is the integration of multiple forms of media, eg., VLC Player, Adobe Flash, Real Player, etc.
ii. Specific purpose software: It is a highly specialised software designed to handle particular tasks. It is also known as customised software.
Free and Open source software
It gives the user the freedom to use, copy, distribute, examine, change and improve the software. Some examples are:
- GNU/Linux is a computer operating system assembled under the model of free and open source software development and distribution.
- GIMP (GNU Image Manipulation Program) is an image editing software.
- Mozilla Firefox is one of the most popular web browsers. It provides added security features for safe browsing.
- OpenOffice.org is a complete office software which contains word processor, spread sheet and presentations.
Refers to copyrighted computer software which is made available for use free of charge for an unlimited period.
Refers to commercial software that is distributed on a trial basis. It is distributed without payment and with limited functionality.
It is a computer program that is an exclusive property of its developer or publisher and cannot be copied or distributed without licensing agreements. It is sold without any access to source code and is therefore not possible to change or improve by the user, eg., MS Windows, Mac OS.
Human ware or live ware
Refers to humans who use computer.