COMPUTER REFRESHER FOR IBPS RRB What is a computer? An electronic device which is capable of receiving data in a particular form and of performing a sequence of operations in accordance with a predetermined but variable set of procedural instructions (program) to produce a result in the form of information. Structure of a computer INPUT UNIT: This unit contains devices with the help of which we enter data into computer. This unit makes link between user and computer. The input devices translate the information into the form understandable by computer.
Following are few of the important input devices which are used in a computer: Keyboard, Mouse, Joy Stick,Light pen, Track Ball, Scanner, Graphic Tablet Microphone, Magnetic Ink Card Reader(MICR),Optical Character Reader(OCR), Bar Code Reader, Optical Mark Reader(OMR). The QWERTY keyboard was invented in 1875, by Christopher Latham Scholes. A standard keyboard has 101 keys. The Computer mouse was invented in 1960, by Douglas Engelbart OUTPUT UNIT: Output unit consists of devices with the help of which we get the information from computer. This unit is a link between computer and users. Output devices translate the computer's output into the form understandable by users. Following are few of the important output devices which are used in a computer. Monitors, Graphic Plotter, Printer CENTRAL PROCESSING UNIT (CPU): CPU is considered as the brain of the computer. CPU performs all types of data processing operations. It stores data, intermediate results and instructions (program). It controls the operation of all parts of computer. CPU itself has following three components Arithmetic & Logic Unit (ALU) Memory Unit Control Unit ARITEMATIC&LOGIC UNIT (ALU):
ALU is the part of a computer that performs all arithmetic computations, such as addition and multiplication and all comparison operations. MEMORY UNIT: Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored. CONTROL UNIT: This unit controls the operations of all parts of computer but does not carry out any actual data processing operations. Functions of this unit are: It is responsible for controlling the transfer of data and instructions among other units of a computer. It manages and coordinates all the units of the computer. It obtains the instructions from the memory, interprets them, and directs the operation of the computer. It communicates with Input/Output devices for transfer of data or results from storage. It does not process or store data. CPU Special Registers The CPU contains a number of special-purpose registers: Instruction Register (IR): The instruction register holds the instruction currently being executed. Memory Data Register (MDR): The memory data register (also known as the memory buffer register or data buffer) holds the piece of data that has been fetched from memory. Memory Address Register (MAR): The memory address register holds the address of the next piece of memory to be fetched.
Program Counter (PC): The program counter holds the location of the next instruction to be fetched from memory. It is automatically incremented between supplying the address of the next instruction and the instruction being executed. Accumulator: The accumulator is an internal CPU register used as the default location to store any calculations performed by the arithmetic and logic unit. Generation of Computers Generation in computer terminology is a change in technology a computer is/was being used. There are totally five computer generations known till date. S.N. Generation & Description 1 First Generation The period of first generation: 1946-1959. Vacuum tube based. 2 Second Generation The period of second generation: 1959-1965. Transistor based. 3 Third Generation The period of third generation: 1965-1971. Integrated Circuit based. 4 Fourth Generation The period of fourth generation: 1971-1980. VLSI microprocessor based. 5 Fifth Generation The period of fifth generation: 1980-onwards. ULSI microprocessor based
Types of computer: Sr. No. Type Specifications 1 PC (Personal Computer) It is a single user computer system having moderately powerful microprocessor 2 WorkStation It is also a single user computer system which is similar to personal computer but have more powerful microprocessor. 3 Mini Computer It is a multi-user computer system which is capable of supporting hundreds of users simultaneously. 4 Main Frame It is a multi-user computer system which is capable of supporting hundreds of users simultaneously. Software technology is different from minicomputer. 5 Supercomputer It is an extremely fast computer which can execute hundreds of millions of instructions per second. Charles Babbage is called the "Father" of the computer. The First mechanical computer designed by Charles Babbage was called Analytical Engine. World s first Supercomputer were introduced in the 1960s, by Seymour Cray at Control Data Corporation (CDC). Performance of a supercomputer is measured in floating point operations per second (FLOPS). Supercomputer with fastest speed is NUDT Tianhe-2 manufactured by China in 2013. PARAM 8000 is considered India's first supercomputer. It was indigenously built in 1990 by Centre for Development of Advanced Computing.
Latest Supercomputer in India developed by Indian Institute of Science, Bangalore name SahasraT (SERC - Cray XC40) speed 901.5 FLOPS world rank 79. Computer Hardware Hardware represents the physical and tangible components of a computer i.e. the components that can be seen and touched. Examples of Hardware are following: Input devices -- keyboard, mouse etc. Output devices -- printer, monitor etc. Secondary storage devices -- Hard disk, CD, DVD etc. Internal components -- CPU, motherboard, RAM etc. Computer Software Software is a set of programs, which is designed to perform a well-defined function. A program is a sequence of instructions written to solve a particular problem. What is open source software? Open source software is software whose source code is available for modification or enhancement by anyone. Example: Linux, Apache, Firefox, MYSQL, PHP, Thunderbird What is Closed Source Software? Closed source software can be defined as proprietary software distributed under a licensing agreement to authorized users with private modification, copying and republishing restrictions. Example: Mac OS X, Photoshop, Windows 7, Skype, Adobe Flash Player, Internet Explorer
Types of software Difference between application software and system software Subject Application Software System Software Definition Application software is System software is computer computer software designed to help the user to perform specific tasks. software designed to operate the computer hardware and to provide a platform for running application software. Purpose Application software is System software is computer
computer software designed to help the user to perform specific tasks. software designed to operate the computer hardware and to provide a platform for running application software. Purpose It is specific purpose software. It is general-purpose software. Classification Package Program, Time Sharing, Customized Program Resource Sharing, Client Server Batch Processing Operating System Real time Operating System Multi-processing Operating System Multi-programming Operating System Distributed Operating System Environment Essentiality Number It executes as and when required. Application is not essential for a computer. The number of application software is much more than system software. It executes all the time in computer. System software is essential for a computer The number of system software is less than application software. Operating System
An operating system (OS) is a collection of software that manages computer hardware resources and provides common services for computer programs. The operating system is a vital component of the system software in a computer system. An operating system is a program that acts as an interface between the software and the computer hardware. It is an integrated set of specialised programs that are used to manage overall resources and operations of the computer. It is specialised software that controls and monitors the execution of all other programs that reside in the computer, including application programs and other system software. Relationship between Hardware and Software Hardware and software are mutually dependent on each other. Both of them must work together to make a computer produce a useful output. Software cannot be utilized without supporting hardware. Hardware without set of programs to operate upon cannot be utilized and is useless. To get a particular job done on the computer, relevant software should be loaded into the hardware Hardware is a one-time expense. Software development is very expensive and is a continuing expense. Different software applications can be loaded on a hardware to run different jobs. A software acts as an interface between the user and the hardware. If hardware is the 'heart' of a computer system, then software is its 'soul'. Both are complimentary to each other. MEMORY
Cache Memory Cache memory is a very high speed semiconductor memory which can speed up CPU. It is used to hold those parts of data and program which are most frequently used by CPU. Advantages The advantages of cache memory are as follows: Cache memory is faster than main memory. It consumes less access time as compared to main memory. It stores the program that can be executed within a short period of time. It stores data for temporary use.
Disadvantages The disadvantages of cache memory are as follows: Cache memory has limited capacity. It is very expensive. Function of different register SI No. Name of register Function 1 Memory Address(MAR) Holds address of the active memory location. 2 Memory Buffer(MBR) Holds information on its way to and from memory. 3 Program Control(PC) Holds address of the next instruction to be executed. 4 Accumulator(A) Accumulates result and data to be operated from. 5 Instruction(I) Holds an instruction while it is being executed. 6 Input/Output(I/O) Communicates with I/O devices. Difference between Primary memory and Secondary memory Primary memory Secondary memory Speed Fast Slow Cost Expensive Cheap Capacity Low capacity Large capacity
Relation with Works directly with the Not connected directly to Processor processor the processor Primary memory is divided into two subcategories RAM and ROM. Difference between RAM and ROM RAM ROM Stands for Random Access Memory Read only memory Use Volatility Types RAM allows the computer to read data quickly to run applications. It allows reading and writing. RAM is volatile i.e. its contents are lost when the device is powered off. The two main types of RAM are static RAM and dynamic RAM. ROM stores the program required to initially boot the computer. It only allows reading. It is non-volatile i.e. its contents are retained even when the device is powered off. The types of ROM include PROM, EPROM and EEPROM. Difference between SRAM and DRAM SRAM DRAM
Definition It is a type of RAM. SRAM essentially uses latches to store charge. It is also a type of RAM. DRAM makes use of capacitors to store bits in the form of charge. Speed Faster Slower Size Bigger Smaller Capacity Less 5 to 10 times more than SRAM Applications Generally in smaller applications like CPU Commonly used as the main memory in personal computers cache memory and hard drive buffers Access Easy Harder Power Consumption Less More Rom has mainly three types: PROM,EPROM and EEPROM. PROM (Programmable Read only Memory) PROM is read-only memory that can be modified only once by a user. EPROM (Erasable and Programmable Read Only Memory) During programming, an electrical charge is trapped in an insulated gate region. For erasing this charge, ultra-violet light is passed through a quartz crystal window(lid). This exposure to ultra-violet light dissipates the charge. EEPROM (Electrically Erasable and Programmable Read Only Memory) The EEPROM is programmed and erased electrically. It can be erased and reprogrammed about ten thousand times. The process of re-programming is flexible but slow.
Secondary Memory This type of memory is also known as external memory or non-volatile. It is slower than main memory. These are used for storing data/information permanently. For example : Hard disk, CD-ROM, DVD etc. Characteristic of Secondary Memory These are magnetic and optical memories It is known as backup memory. It is non-volatile memory. Data is permanently stored even if power is switched off. It is used for storage of data in a computer. Computer may run without secondary memory. Slower than primary memories. Hard disk It is used as main storage device of the computer. It uses 2-4 metallic disk (platter). The disk is usually made of aluminum. It has the storage capacity of few mega bytes to tera byte. CD It stands for Compact Disk. It has storage capacity of 700 MB or approximately 90 minutes of standard audio. Types of CD are CD-R is a blank CD in which data can be stored once. After storing data it is converted into CD- ROM. CD-ROM It cannot be erased or updated CD-RW it can be erased and used for multiple times. DVD
It stands for Digital Versatile Disk. It has the storage capacity of 4.7GB to 17GB. Its shape and size is similar to CD but the difference in storage capacity is due to different chemical component and data is compressed before storing. Pen drive It is a flash memory. It is a semi-conductor memory. It is mainly used for transferring data. It has faster read/write speed compared to magnetic memory. Pen drive has storage capacity of few MB-GB. A pen drive is a plug and play device. A pen drive can be connected with the computer through USB port. Computer languages A programming language is a special language use to develop applications, scripts, or other set of instructions for computers to execute. Machine Language Machine language or machine code is a set of instructions executed directly by a computer's central processing unit (CPU). Assembly Language Assembly language is a low-level programming language for a computer or other programmable device specific to a particular computer architecture in contrast to most high-level programming languages, which are generally portable across multiple systems. Difference between High-Level & Low-Level Language High-level Language Low-level languages Learning Understanding Execution Modification Uses High-level languages are easy to learn. High level languages are near to human languages. Programs in high-level languages are slow in execution. Programs in high-level languages are easy to modify. These languages are normally used to write application programs. Low-level languages are difficult to learn. Low-level languages are far from human languages. Programs in low-level languages are fast in execution. Programs in low-level languages are difficult to modify. These languages are normally used to write hardware programs.
Special purpose language A special purpose language is a program language that was designed for a specific function. For example, LISP is an example of a special purpose programming language designed to create artificial intelligence. Examples of High level languages are BASIC, COBOL, C, C++, Pascal, Prolog and JAVA COBOL stands for Common Business Oriented Language for business data processing. Fortran: The name FORTRAN is an acronym for FORmula TRANslation, because it was designed to allow easy translation of math formulas into code. The C is a general-purpose, procedural, imperative computer programming language developed in 1972 by Dennis M. Ritchie at the Bell Telephone Laboratories to develop the UNIX operating system. Difference between source code and objet code S. No. Source code Object code 1 Source code is written in highlevel or assembly language. 2 Source code is easy to understand. Object code is written in machine language through compilers. Object code is difficult to understand 3 Source code is easy to modify. Object code is difficult to modify 4 Source code contains fewer statements than object code. Object code contains more statements than source code. Language translator Language translator is a program that translates a program of high level language of computer understands only machine language. A program written in high-level or assembly language cannot be run on a computer directly. It must be converted into machine language before execution.
Types of translators 1. Compiler A compiler is a program that converts the instruction of a high level language into machine language as a whole. Or, The compiler converts the source program into machine code as a whole. 2. Interpreter An interpreter is a program that converts one statement of a program into machine at one time. The advantage of interpreters over compilers is that an error is found immediately. So the programmer can correct errors during program development. The disadvantage of interpreter is that it is not very efficient. 3. Assembler An assembler is translating program that translates the instruction of a assembly language into machine language. Microsoft word Word Processing Software Word processing software is used to manipulate a text document, such as a resume or a report. Some of the functions of word processing software include: Creating, editing, saving and printing documents. Copying, pasting, moving and deleting text within a document. Formatting text, such as font type, bolding, underlining or italicizing. Creating and editing tables. Inserting elements from other software, such as illustrations or photographs. Correcting spelling and grammar. Microsoft word shortcut keys: Shortcut Ctrl + N Ctrl + W Ctrl + S Ctrl + P Ctrl + F Description Starts a new blank document Close the active document Save a document Display the print dialog box. Open find box.
Ctrl + Page Up Ctrl + Page Down Backspace Ctrl + Backspace Deletes Ctrl + Delete Ctrl + Z Ctrl + Y Ctrl + X Ctrl + C Ctrl + V Ctrl + A Ctrl + B Ctrl + I Ctrl + U Ctrl + Shift + L Ctrl + Shift + F Ctrl + Shift + > Ctrl + ] Ctrl + Shift + < Ctrl + [ Ctrl + <left arrow> Ctrl + <right arrow> Ctrl + <up arrow> Ctrl + <down arrow> Ctrl + Shift + F6 Ctrl + Shift + F12 F1 F7 F12 Shift + Alt + D Shift + Alt + T Move to the previous edit location Move to the next edit location Deletes one character to the left Deletes one word to the left Deletes one character to the right Deletes one word to the right Undo last action. Redo the last action performed. Cut selected text. Copy selected text. Paste. Select all contents of the page. Bold highlighted selection. Italic highlighted selection. Underline the selected text. Quickly create a bullet point. Change the font. Increase selected font +1pts up to 12pt and then increase font +2pts. Increase selected font +1pts. Decrease selected font -1pts if 12pt or lower; if above 12, decreases font by +2pt. Decrease selected font -1pts. Moves one word to the left. Moves one word to the right. Moves to the beginning of the line or paragraph. Moves to the end of the paragraph. Switches to another open Microsoft Word document. Prints the document. Open Help. Spellcheck and grammar check selected text or document. Save As. Insert the current date. Insert the current time. Computer network and security Difference between Internet and Intranet. Internet 1. Internet is network of Computers which is open for all.
2. Internet itself contains a large number of intranets. 3. Unlimited number of users. 4. Visitors traffic is unlimited. 5. Contains unlimited source of information. 6. Collection of various LANs, WANs and MANs. Intranet 1. Intranet is network of Computers designed for a specific group of users. 2. Intranet can be accessed from Internet but with restrictions. 3. Limited number of Users. 4. Limited visitors traffic. 5. Contains only specific group purpose information. 6. Mostly any of LAN or MAN or WAN. LAN MAN Difference Between LAN, MAN and WAN 1. LAN (Local Area Network) is a group of computers and other network devices which are connected together. 2. All the devices that are part of LAN are within a building or multiple building. 3. LAN network has very high speed mainly due to proximity of computer and network devices. 4. LAN connection speeds can be 10Mbps or 100Mbps or 1000Mpbs also. 5. LAN uses Guided Media 1. MAN ((Metropolitan Area Network) is a larger network of computers and other network devices which are connected together usually spans serveral buildings or large geographical area. 2. All the devices that are part of MAN are span across buildings or small town. 3. MAN network has lower speed compared to LAN. 4. MAN connection speeds can be 10Mbps or 100Mbps. 5. MAN uses Guided Media or Unguided media. WAN 1. WAN (Wide Area Network) is a group of computers and other network devices which are connected together which is not restricted to a geographical location. Internet is WAN 2. All the devices that are part of WAN have no geographical boundaries.
3. WAN speed varies based on geographical location of the servers. WAN connects several LANs 4. WAN connection speeds can be 10Mbps or 100Mbps. 5. WAN mainly uses Guided Media or Unguided media. Its long distance communications, which may or may not be provided by public packet network. Open Systems Interconnection (OSI) model OSI (Open Systems Interconnection) is reference model for how applications can communicate over a network. The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create will interoperate, and to facilitate clear comparisons among communications tools. There are seven layers in the OSI model, each having a different task. Difference Between Virus and Worm
How does it infect a computer system? How can it spread? Does it infect files? whose speed is more? Definition Virus It inserts itself into a file or executable program. It has to rely on users transferring infected files/programs to other computer systems. Yes, it deletes or modifies files. Sometimes a virus also changes the location of files. Virus is slower than worm. The virus is the program code that attaches itself to application program and when application program run it runs along with it. Worm It exploits a weakness in an application or operating system by replicating itself. It can use a network to replicate itself to other computer systems without user intervention. Usually not. Worms usually only monopolize the CPU and memory. Worm is faster than virus. Eg.The code red worm affected 3 lakhs PCs in just 14 Hrs. The worm is code that replicate itself in order to consume resources to bring it down. Trojan horse In computers, a Trojan horse is a program in which malicious or harmful code is contained inside apparently harmless programming or data in such a way that it can get control and do its chosen form of damage, such as ruining the file allocation table on your hard disk. What is Anti-Virus Software? Anti-virus software is a program or set of programs that are designed to prevent, search for, detect, and remove software viruses, and other malicious software like worms, trojans, adware, and more.