Chapter 2

 The hardware and software is used as unit to process data is called computer system.  Hardware Input Devices CPU Output Devices Storage  Software A set of instructions given to computer to solve a problem is called software. Software is also called program Computer works according to the instructions written in software

 Input devices  The data or instruction given to the computer is called input.  A hardware component used to enter data and instruction into computer is called input device  Output Devices  The data processed into useful information is called output.  A hardware component used to display information to the user is called output devices.

 System Unit  System unit is a box that contains different electronics components of a computer system.  The electronics components in the system unit are connected to the motherboard.  Important components of system unit are CPU and memory  Storage  The hardware components used to store data, instruction and information permanently are called storage devices.  Examples: Hard Disk, floppy Disk, CD, DVD, etc

 The data or instruction given to the computer is called input.  A hardware component used to enter data and instruction into computer is called input device  Types of input Devices  Keyboard  Mouse  Trackball  Touchpad/Track pad  Pointing Stick  Graphic Tablet  Touch Screen  Digital Scanner  Digital Camera  Joystick

 Hardware components that are used to receive information from the computer are called output devices.  Output devices take information from the computer and convert it in a form that is understandable by users.  Printers  Plotter  Display devices  Speaker& Headsets  Data Projrctors

 Printer is an output device that prints characters, symbols and graphics on paper.  Printed output is called hardcopy.  There are two types of printers.  Impact Printers Dot Matrix Printers Daisy wheel printers Line Printers  Non-Printers Laser Printer Inkjet Printer

 Impact printer works like a typewriter.  Prints characters or images by striking print hammer or set of pins against an inked ribbon.  Ink is pressed from ribbon on the paper to produce the output.  Impact printers are used where low-cost printing is required.

 Produces printed images when tiny pins on a print head strike an inked ribbon.  When ribbon presses against the paper it creates dot that form characters and graphics.  Contains 9 to 24 pins.  Higher number of pins creates more dots that produce high quality image.  Speed of most dot-matrix printer ranges from 350 to 1100 characters per second.

 It uses a print wheel. Print wheel is called daisy wheel.  Each petal of daisy wheel contains characters  A motor rotates the wheel.  A hammer strikes a petal against the ribbon when the desired character reaches the position on the paper.  This prints the character on the paper.  Slower than dot matrix printer but better in quality

 Line printer is a fast impact printer.  It can print multiple characters on the same line at a time.  Its speed is measured in line per minute.  Speed range of line printer is from 300LPM to 2400LPM  Faster than dot matrix and daisy wheel.  More noisy and provide limited font capability.  Example:Band printer and chain printer

 A non impact printer prints characters and graphics on paper without striking paper.  The characters are printed on paper with some mean such as laser  Some printers use spray in while other use heat and pressure to create images.  These printers are faster than impact printer.  More costly than impact printers.  Produce no noise during printing  Print quality is better than impact printers

 Light Amplification by stimulated emission of radiation.  Similar to a photocopying machine.  Uses laser beams to burn special powder on page to create a permanent image.  Prints a complete page at a time  Typical laser printer provides a resolution 0f 1200 DPI or more.  Produces very high quality prints.  Printing speed of laser printer ranges from 12 to 45 ppm

 It prints characters and graphics by spraying tiny drops of liquid ink on paper.  These printers can produce quality text and graphics in both black and white and color.  Typical inkjet printer provides resolution of 600DPI or more.  Slower than laser printer.  Printers can print from 10 to 35 ppm.  Inexpensive than laser printer

 Plotter is an output devices that is used to produce image quality graphics in variety of colors.  Plotters are used to create maps, architectural drawings, graphs and charts.  A plotter works by drawing lines on paper using pens held in a mechanical arm.

 Monitor is most common output device.  The output displayed by monitor is called soft copy.  Looks like a television and displays text and graphics.  Different display screen can be distinguished on the following features.  Size  Color  Resolution  Refresh rate  Dot Pitch  Display Adapter

 Cathode Ray Tube  It can display text and graphics  It used CRT that creates an image by an electronic beam.  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.  CRT in color monitor consists of three guns RGB

 Laptop PCs use flat panel monitors  These monitor take less space.  Flat panel monitor use a variety of technologies  Common technology is Liquid Crystal display  LCD monitor use much less power than CRT.  These are available in different sizes such as 15, 17, 19, 21, 32 and so on.

 A type of output produced in the form of sound, voice or music is known as audio output.  Speakers and headsets are two commonly used audio outputs.  Many personal computers have internal speaker.  Headsets are also used to produce audio output

 CPU is the brain of Computer  It is the most important component of a computer  It is also called processor  A computer cannot work without CPU  CPU is located of Mother Board  Performs operations on data according to the given instructions  It can performs arithmetic and logical operations  It executes and controls the computer hardware

 ALU(Arithmetic and Logic unit)  Performs basic arithmetic functions such as addition subtraction multiplication and division  Logic unit perform logical operations like comparing two data items to find which is greater  CU(Control Unit)  It generates signal to direct the entire computer system  It controls and coordinates all activities of computer system.  It does not executes program instructions  Control unit communicates with arithmetic and logical unit and other parts

 A small high speed memory inside CPU  CPU contains number of registers  Registers are used to store information being processed.  Temporary storage area of instruction or data  Temporary results during processing are also stored in registers  Each registers has a predefined function

 Data in digital computers is represented as a collection of bits.  The smallest unit of data that can be used by computer is called bit.  A set of 8bit is called byte.  One byte is required to store one character.

 Different types of memories are random access memory and read-only memory  RAM(Random Access Memory)  It is also called Main Memory or Direct Access Memory  Each individual byte in the entire memory is directly accessible.  Program must be loaded into RAM before execution  RAM is Volatile  ROM(Read Only Memory)  Instructions in ROM prepare the computer for use.  Contents of ROM can only be read but cannot be changed or deleted.  It stores data and instructions permanently  ROM is NON-Volatile

 DRAM  Dynamic Random Access Memory  It is a type of memory that is used in most computers  Least Expensive kind of memory.  It requires an electric current to maintain its electrical state.  Electrical charge of DRAM decreases with time that may result in loss of data.  DRAM is recharged or refreshed again and again to maintain data.  Processor cannot access data of DRAM when its being refreshed.

 Static Random Access Memory  It can store its value without any need to refresh the data.  Expensive type of memory  CPU does not wait to access data so it is faster.  It utilizes more power than DRAM  It is normally used to built faster cache memory.

 PROM  Programmable Read-only Memory  This form of ROM is initially blank  Manufacturer can write data on it using special device  The user can write data and instruction only once  If there is an error chip becomes unusable  EPROM  Erasable Programmable Read Only Memory  Program and data written on it can be erased using ultraviolet rays.  EEPROM  Electronically erasable Programmable ROM  User can erase and write instruction using electrical devices  Contents can be modified easily

 Cache Memory  Designed to speed up the transfer of data and instructions.  It is located inside or close CPU.  Faster than RAM.  Data and instruction that are most recently or frequently used by CPU  Data and instructions are retrieved from RAM when CPU uses them for first time.