Introduction to Computer System

. INTRODUCTION

A computer is a programmable device which responds to a specific set of instructions in a well-defined manner and executes a prerecorded list of instructions. A computer is an electronic device which takes input from the user, processes it, stores it and gives output in desired form. The computer as a system is a combination of hardware and software components that jointly offer the necessary services to the user. Computer is derived from the Latin word ‘Computare’ which means ‘to calculate’.


COMPUTER SYSTEM

Computer System is a group of physical parts that are integrated to achieve the objectives. A complete computer system consists of 4 parts: hardware, software, people, and data.
Two principal characteristics of computer:
• It responds to a specific set of instructions in a well defined manner.
• It can execute a prerecorded list of instructions (a program).
A computer system needs to do the following operations:
 Input: i.e. to accept the data/instructions from users
 Process: i.e. to process the data
 Storage: i.e. to store or holds the data
 Output: i.e. to provide the final result to users.

This cycle of operation of a computer is referred as Input-Process-Output or IPO cycle.

A complete computer system consists of 4 parts:
1) Hardware
2) Software
3) One or more users.
4) Data.

COMPUTER ARCHITECTURE

Every computer is constructed by combining various parts. All these parts work in an organized way to perform calculations, organize data, and communicate with other computer systems. The design, arrangement, construction or organization of the different parts of a computer system is called as “computer architecture”.

Computer system architecture (Anatomy) is concerned with the structure of computer. In other words, the style of construction & organization of many parts of the computer system is called as “computer architecture”.
Computer System Architecture consists of the various components such as:
 Input Unit
 Central Processing Unit (CPU)
 Memory Unit (MU)
 Output Unit

HARDWARE AND SOFTWARE
Hardware refers to all the physical parts that make up a computer. That is, all the electric, electronic, and mechanical devices of the computer are hardware. Examples of hardware are keyboard, mouse, monitor, and printer. So, hardware is those parts of the computer, which we can touch.

Software is a set of electronic instructions that make computer perform tasks. In other words, software tells the hardware what to do. Without software, hardware is useless. Hardware needs instructions to process data into information. Those instructions are supplied from software.

Software is also referred to as a set of program. Computer uses varieties of programs. Some programs are developed for computer’s own use and internal maintenance. Other types of programs are used for calculating and processing data.
Relationship between Hardware and Software
1. Both hardware and software are necessary for a computer to do useful job. Both are complementary for each other.
2. The same hardware can be loaded with different software to make a computer system perform different types of jobs, just as different songs can be played using same cassette player.
3. Except for upgrades (like increasing the main memory and hard disk capacities, or adding speakers, modems etc.), hardware is normally a one-time expense, whereas software is a continuing expense. Just as we buy new cassettes for the newly released songs, or songs whose cassette we do not have, similarly one buys new software to be run on the same hardware, as and when need arises or funds become available.





USERS AND DATA
Users
• People or computer operators.
• Some computer systems are complete without person’s involvement; no computer is autonomous.
• Even if a computer can do its job without person, people still design, build, program & repair computer system.
Data
• Individual facts or bits of info, which by themselves may not make much sense to person.
• Computer reads and stores data of all kinds whether words, numbers, images, or sounds in the form of numbers.
• Computerized data, digital, means it has been reduced to digits or nos.
• Following instructions from software and users, the computer manipulates data by performing calculations, doing comparisons, or arranging the bits of info so they make sense to user.
• Data are organized into files.
• File that user can open and use is a document.
• Computer document can be text file (letter), group of numbers (a budget), video clip (images and sounds) or any combination of these items.

2. CHARACTERISTICS OF COMPUTERS

1. Speed: The speed of a computer is incredibly faster than what man can possibly record or calculate normally.The speed of computer for performing a single operation can be measured in terms of Milliseconds, Microseconds, Nanoseconds and Picoseconds.
1/1000 or (10-3) sec……………………………..1 Millisecond (ms)
1/1000000 or (10-6) sec………………………....1 Microsecond (µs)
1/1000000000 or (10-9) sec …………………….1 Nanosecond (ns)
1/000000000000 or (10-12) sec…………………1 Picosecond (ps)
1/000000000000000 or (10-15) sec……………..1 Femtosecond (fm)

2. Storage: One of man's failing is perhaps his inability to remember and "store" large volumes of information in his brain. The computer is capable of overriding this deficiency as it can store. The storing capacity is measured in terms of Bytes, Kilobytes, Megabytes, Gigabytes and Terabytes.
4 bits………………………..................................1 Nibble
8 bits………………………..................................1 Byte
1024 Bytes ............................................................1 Kilobyte (KB)

1024 Kilobytes.......................................................1 Megabyte (MB)
1024 Megabytes.....................................................1 Gigabyte (GB)
1024 Gigabytes .....................................................1 Terabyte (TB)

3. Word Length: A word is simply a fixed-sized group of bits that are handled together by the machine. The number of bits in a word (the word size or word length) is an important characteristic of a computer system. The majority of the registers in the computer are usually word-sized. The amount of data transferred between the processing part of the computer and the memory system is most often a word.The size of the registers, which sometimes is called the word length (or word size); indicate the amount of data with which the computer can work at given time. The bigger the word size, the more quickly the computer can process the set of data. Occasionally, you will hear people refer to “32-bit processors” or “64-bit processors” or even “64-bit computers”. This terminology refers to the size of registers in the processor. If the entire factors are kept equal, a CPU with 32-bit registers can process data twice as fast as one with 16-bit registers.

4. Accuracy and Reliability: Inspite of high speed, the computers are quite accurate and reliable in their calculations. The accuracy of operation of a computer is always 100%. Computer is only a machine and does not make error on its own. It is thus reliable. Computer can perform all the calculations and comparisons accurately. Sometimes, errors may be produced by computers due to the fault in the machine or due to mistakes in the programs. If the input data are not correct, this may also lead to incorrect output.

5. Automatic: Once the process has been initiated, computer is quite capable of functioning automatically. It does not require a prompt from an operator at each stage of the process. Computer is an automatic machine. Everything that is given to computer are processed and done by computer automatically according to the instruction provided.

6. Versatility: Computer has a wide range of application areas i.e., computer can do many types of jobs. It can perform operations ranging from simple mathematical calculations to highly complex and logical evaluations for any extended period of time. Some of the application areas of computers are Education, Science and Technology, Business, Medicine, Astronomy etc.

7. Diligence: Man suffers from physical and mental fatigue, lack of concentration and laziness which do not permit him to carry on his task at the same level of speed and accuracy through the entire day. The computer, on the other hand is capable of operating at exactly the same level of speed and accuracy even if it has to carry out the most voluminous and complex operations for a long period of time. A computer can perform repetitive tasks without being bored, tired and losing concentration. It can continuously work for several hours without human intervention after the data and programs are fed to it. There is no ageing effect on computer i.e. efficiency does not decrease over the years of use.

3. TYPES OF COMPUTERS

Desktop Computer
• Easily fit on a normal size office table or a desk.
• Generally designed to be used by one person at a time.
• Commonly used and can be found everywhere like offices, classrooms, homes, hospitals, shops etc.
• Eg: Apple, IBM, Compaq Presario, Dell, Zenith, Siemens, Toshiba etc.
• Two common design for desktop computers:
1) Traditional desktop model features a horizontally oriented system unit on top of which users place monitor.
2) Vertically oriented tower model have become the more popular style of desktop systems.

Notebook Computers
• Also called as Laptops.
• Easy to carry from one place to another.
• Light weight but incorporate all basic features of computer like Display, keyboard, trackball or pad, hard disk, Floppy Disk, CD and DVD Drives.
• Use LCD (Liquid Crystal Display) monitors.
• Can operate with AC power or battery power also.

Personal Digital Assistance (PDA)
• PDAs are also called palmtops, hand-held computers and pocket computers
• Powerful hand held communication intensive device with a focus on ease of use.
• Smaller than laptops that fits in our palm
• Normally used for taking notes, displaying telephone no., keeping tracks of dates and meeting, etc.
• Consists of an electronic writing pad and a light-sensitive electronic pen.
• Eg: Apple’s Newton, Compaq, etc.

LIMITATIONS OF COMPUTERS
1. Sometime the failure in devices and programs can produce unreliable information.
2. Computer is a dull machine. It doesn’t have intelligence on it.
3. It cannot operate without human involvement.
4. Computers lack emotions.

ADVANTAGES AND DISADVANTAGES OF COMPUTERS
Advantages
a. Computers are always accurate and reliable than human.
b. They are faster than human in calculations.
c. They never feel exhausted and tired like human being.
d. They can perform complicated and difficult works which are hard for us.
e. They are versatile i.e. master in all types of work and fields like education, hospital, banks, etc.
f. It is used for communication between many peoples.

Disadvantages
a. They cannot operate without batteries or electricity.
b. Failure in devices and wrong information by users makes it unreliable.
c. It is an expensive device.
d. They can be used for computer crimes like hacking, sending viruses, etc.

4. USES OF COMPUTER IN DIFFERENT FIELDS

1. Banking: Banks use computer for general-purpose computations, to handle transaction. These days bank provide the ATM service where user can withdraw their money any time from ATM machine by using the ATM card.

2. Commercial Enterprises: Many business companies use computer to help in the control of their day-to-day transaction. Computers are used for keeping record of the employees, managing the stock of company, etc.

3. Communication: Computers are massively used in communication. Communicating is done by emails, chatting, videoconference, e-fax, etc with the help of internet.

4. Desktop Publishing System: A desktop publishing package is more powerful, attractive and efficient than word processor package. The system includes computer and a number of peripherals with powerful software that can produce various layouts with pictures and text printed in a variety of attractive way, which are used in manuals, bulletins, newsletters etc.

5. Education: Computers are used as teaching aid, information resource, and computing and research tool. When computer is used as a teaching aid, it is referred to as Computer Assisted Instruction (CAI). Software for CAI can be prepared in a variety of modes, such as tutorial, discovery, problem solving, modeling, and drilling and practice modes.

6. Health and Medical Field: Computers are widely used in hospitals to help doctors in diagnosis, getting information on patients, diseases, treatment, drugs, keeping patient’s record etc. Examples: Magnetic Resonance Imaging (MRI), CT scan machine, Eye testing machines, Ultrasonic machine, etc.

7. Home: Home computers can be used in recreational activities. Home computers can also be used in storing personal information such as birth dates, addresses, telephone numbers, photo albums, to keep the record of family expenses etc. People use home computers to listen songs, watching movies, accessing the Internet, etc.

8. Industries: Computers are extensively used in industries for automatic control of machines, process, measurement and display of electrical and physical quantities.

9. Military: Smart weapons use microprocessor-based control systems. Modern tanks, torpedoes, missiles etc. employ computerized control systems. A guided missile uses internal computer for its control.

10. Multimedia: In recording and film studio computer are used intensively. The music can be recorder in different tracks and later merge to a single music. Movie editing can be done frame by frame.

11. Office: Computers are used in preparing reports, memorandum, and copy of advertisement, letter, publicity, contracts, forms, notes, and notices etc., which are the basic works of an office. Computer helps user in preparing, storing, retrieving and displaying text. In offices accounting, billing preparation of payrolls, data analysis, auditing, investment, inventory control, preparation of budgets, sales analysis etc. are also performed. In most of the computerized offices, word processing and spread applications are used.

12. Research: Scientific and engineering design and research work involve complex and massive computations. So computers are must for this type of work.

13. Simulation: Computer simulation involves typing to predict what will happen in a real-life situation from model of that situation. Computer Aided Design (CAD) is widely used in the design of electronic circuits, ships, roads cars etc.

5. INPUT / OUTPUT DEVICES

a. Input Device
The raw data & program are entered in the computer through input device. It reads the raw data prepared by the user & sends then into the computer as a series of electronic pulses. The devices which, read the data and program into the computer, are called input devices, i.e., data and programs are entered into the computer system for processing through input device. An input device converts input data into suitable form acceptable to a computer. So, it is a means of communication between user and the computer. Examples of input devices are keyboard, mouse, joysticks, optical character reader, light pen, touch panel.

An input device is any peripheral (piece of computer hardware equipment) used to provide data and control signals to an information processing system (such as a computer).

i. Keyboard:
A keyboard is the primary & most user-friendly input device. Both data & instructions can be entered into the computer with the help of the keyboard. It is an essential device for interactive processing in the sense that the user can issue commands through the keyboard to the CPU & receive the response immediately on monitor. Computer keyboards are similar to typewriter keyboards but contain additional keys. There are separate keys for each number, letters & symbols. The data can be sent to the CPU either serially or in parallel. The keyboards therefore can be divided into two types: serial keyboard & parallel keyboard.
At microcomputer level, IBM personal computer has three different PC keyboards-
1. XT (Extended Technology):
It has 83 keys.
2. AT (Advanced Technology):
It has 101 keys.
3. Enhanced Keyboard:
It has 103 keys.

Alphanumeric Keys Letters and numbers along with Tab, Caps Lock, Backspace and Enter
Modifier Keys Shift, Ctrl, Alt
Function keys F1, F2, F3, F4, F5, F6, F7, F8, F9, F10, F11, F12
Numeric Keypad Ten digits (0-9) and mathematical operators (*, -, /, +, %, }, {, <, >, ?, etc)
Cursor-Movement Keys Arrow keys, Home/End and Page Up/Page Down
Special-Purpose Keys Insert, Delete, Esc, Print Screen, Scroll Lock, Pause, Start and Shortcut



How the Computer Accepts Input From the Keyboard?
(read this topic from Peter Norton’s Book)

Use: The various uses of computer keyboard are:
i. In normal usage, the keyboard is used to type text or numbers into a word processor, text editor, or other program.
ii. Keyboards are also used for computer gaming, either with regular keyboards or by using special gaming keyboards which can expedite frequently used keystroke combinations.
iii. A keyboard is also used to give commands to the operating system of a computer, such as the Control-Alt-Delete combination, which brings up a task window or shuts down the machine.

ii. Mouse:
Mouse was invented by Douglas Engelbert of Standford Research Center in 1963 & pioneered by Xerox in the 1970's. It is hand held device with a roller on its base is moved over the surface. As the ball is moved over the surface in any direction, the motion is converted to digital values & is used to determine the direction & magnitude of the mouse's cursor on the screen.

Mouse is one of the most widely used input devices of the computer. A mouse is a small had held device whose relative motion across the surface can be measured. Because mice are the relative devices, they can be picked up; move and then put down again without any changes in reported position. For this the computer maintains the current mouse position, which is incremented or decremented by the mouse movement.

Mouse is a small plastic box with two or three buttons on the top and a ball at the bottom, which rolls on a flat surface. As the ball moves across flat surface (mouse pad), the visible indicator (i.e. pointer/cursor) on the screen, moves in the direction of mouse movement. We can select the commands, draw pictures, and edit text etc. by pressing the mouse button. The mouse is important for graphical user interface because we can simply point to options or objects & click a mouse button. Such applications are often called point & click programs.

There are basically three types of mice-
Mechanical Mouse
Mechanical mouse has a rubber or metal ball on its underside that can roll in all directions. Mechanical sensors within the mouse detect the direction of rolling ball & move on the screen accordingly.

Optomechanical Mouse
Optomechanical mice are same as a mechanical mouse but uses optical sensors to detect motion of the ball. A ball rolls on two shafts. The shaft turns optical shaft-angle encoders to convert motions to electrical signals. This type of mouse is easier to clean as compared to clean a mechanical mouse.

Optical Mouse
The optical mouse is used on a special pad having grids of altering light and dark lines. A LED on the bottom of the mouse directs a beam of light down onto the pad, from which it is reflected and sensed by the detectors on the bottom of the mouse. As the mouse is moved, the reflected light beam is broken each time a dark line is crossed. The number of pulses so generated, which is equal to the number of lines crossed, is used to report mouse movements to the computer.

Mouse can be connected to PC in one of the three ways.
1. Serial mouse connect directly to the serial port (9-pin).
2. PS/2 mouse connect directly to the PS/2 port (6-pin).
3. Cordless mouse does not connect physically but can be connected with infrared or radio waves.

Using the mouse involves five techniques:
1. Pointing: Move the mouse to move the on-screen pointer.
2. Clicking: Press and release the left mouse button once.
3. Double-clicking: Press and release the left mouse button twice.
4. Dragging: Hold down the left mouse button as you move the pointer.
5. Right-clicking: Press and release the right mouse button

Use: The various uses of computer mouse are:
i. A mouse enables us to draw or point on the screen.
ii. We can select the commands, draw pictures, and edit text etc. by pressing the mouse button.

iii. Microphone:
A microphone attached to the computer enables us to add the sound of a voice or a music selection. The microphone gives a signal to the computer/radio/whatever we are using.
A microphone, sometimes referred to as a mic or mike, is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Microphones are used in many applications such as telephones, tape recorders, hearing aids, motion picture production, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, and for non-acoustic purposes such as ultrasonic checking.

b. Output Device

CPU processes the information that is entered through the input devices and produces the meaningful information. These information can appear in variety of form – as a binary number, as picture, as text, as sound or as printed pages. An output device is any device that is capable of representing that information from the computer. Output device includes monitors, speaker, printers, plotters, etc.
Any peripheral that receives and/or displays output from a computer. An output device is any piece of computer hardware equipment used to communicate the results of data processing carried out by an information processing system (such as a computer) to the outside world.

Softcopy Output devices: Softcopy output refers to the output displayed on the screen. The output on the screen is lost when computer is turned off. The most common output device is monitor. Sound produced by voice output device (speaker) is also softcopy output.

Hardcopy Output devices: Hardcopy output refers to recording letters, graphics or pictures on a permanent medium such as paper. Such output can be read immediately or stored and read later. The most commonly used hardcopy output devices are printers and plotters.

i. VDU (Monitors): Visual Display Unit (or monitor), also called display screen, is a most commonly used output device that produces soft copy output. A visual display unit (also called VDU, monitor, or screen) offers a two-dimensional visual presentation of information. a device that display information on a screen.

Classification of Monitors – based on colors
Monochrome Monitor
Monochrome Monitor can display only two colours. The color can be black and white, black and green, amber (brown yellow color) and black.
Gray-scale Monitor
A Gray-Scale monitor is special type of monochrome monitors capable of displaying different shade of Gray.
Color Monitor
Color monitor can display anywhere from 16 colors to 16 millions colors. Colors monitors are some times called RGB monitors because they accept three signals – red, green, and blue.

Classification of monitors – based on technology
CRT (Cathode Ray Tube) Monitors
Flat Panel Display Monitors