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comuter system

The Computer System
Computer is an electronic device that accepts data as input, processes the input data by performing mathematical and logical operations on it, and gives the desired output. The computer system consists of four parts—(1) Hardware, (2) Software, (3) Data, and (4) Users. The parts of computer system are shown in Figure 1.13.
Figure 1.13. Parts of computer system
[View full size image]


Hardware consists of the mechanical parts that make up the computer as a machine. The hardware consists of physical devices of the computer. The devices are required for input, output, storage and processing of the data. Keyboard, monitor, hard disk drive, floppy disk drive, printer, processor and motherboard are some of the hardware devices.
Software is a set of instructions that tells the computer about the tasks to be performed and how these tasks are to be performed. Program is a set of instructions, written in a language understood by the computer, to perform a specific task. A set of programs and documents are collectively called software. The hardware of the computer system cannot perform any task on its own. The hardware needs to be instructed about the task to be performed. Software instructs the computer about the task to be performed. The hardware carries out these tasks. Different software can be loaded on the same hardware to perform different kinds of tasks.
Data are isolated values or raw facts, which by themselves have no much significance. For example, the data like 29, January, and 1994 just represent values. The data is provided as input to the computer, which is processed to generate some meaningful information. For example, 29, January and 1994 are processed by the computer to give the date of birth of a person.
Users are people who write computer programs or interact with the computer. They are also known as skinware, liveware, humanware or peopleware. Programmers, data entry operators, system analyst and computer hardware engineers fall into this category.
1.7.1. The Input-Process-Output Concept
A computer is an electronic device that (1) accepts data, (2) processes data, (3) generates output, and (4) stores data. The concept of generating output information from the input data is also referred to as input-process-output concept.

The input-process-output concept of the computer is explained as follows—
• Input The computer accepts input data from the user via an input device like keyboard. The input data can be characters, word, text, sound, images, document, etc.
• Process The computer processes the input data. For this, it performs some actions on the data by using the instructions or program given by the user of the data. The action could be an arithmetic or logic calculation, editing, modifying a document, etc. During processing, the data, instructions and the output are stored temporarily in the computer’s main memory.
• Output The output is the result generated after the processing of data. The output may be in the form of text, sound, image, document, etc. The computer may display the output on a monitor, send output to the printer for printing, play the output, etc.
• Storage The input data, instructions and output are stored permanently in the secondary storage devices like disk or tape. The stored data can be retrieved later, whenever needed.
1.7.2. Components of Computer Hardware
The computer system hardware comprises of three main components —
1. Input/Output (I/O) Unit,
2. Central Processing Unit (CPU), and
3. Memory Unit.
The I/O unit consists of the input unit and the output unit. CPU performs calculations and processing on the input data, to generate the output. The memory unit is used to store the data, the instructions and the output information. Figure 1.14 illustrates the typical interaction among the different components of the computer.
Figure 1.14. The computer system interaction


• Input/Output Unit The user interacts with the computer via the I/O unit. The Input unit accepts data from the user and the Output unit provides the processed data i.e. the information to the user. The Input unit converts the data that it accepts from the user, into a form that is understandable by the computer. Similarly, the Output unit provides the output in a form that is understandable by the user. The input is provided to the computer using input devices like keyboard, trackball and mouse. Some of the commonly used output devices are monitor and printer.
• Central Processing Unit CPU controls, coordinates and supervises the operations of the computer. It is responsible for processing of the input data. CPU consistsofArithmetic Logic Unit (ALU) and Control Unit (CU).
o ALU performs all the arithmetic and logic operations on the input data.
o CU controls the overall operations of the computer i.e. it checks the sequence of execution of instructions, and, controls and coordinates the overall functioning of the units of computer.
Additionally, CPU also has a set of registers for temporary storage of data, instructions, addresses and intermediate results of calculation.
• Memory Unit Memory unit stores the data, instructions, intermediate results and output, temporarily, during the processing of data. This memory is also called themain memory or primary memory of the computer. The input data that is to be processed is brought into the main memory before processing. The instructions required for processing of data and any intermediate results are also stored in the main memory. The output is stored in memory before being transferred to the output device. CPU can work with the information stored in the main memory. Another kind of storage unit is also referred to as the secondary memory of the computer. The data, the programs and the output are stored permanently in the storage unit of the computer. Magnetic disks, optical disks and magnetic tapes are examples of secondary memory.
Introduction
When we talk of computer hardware, the three related terms that require introduction are—computer architecture, computer organization and computer design. Computer architecturerefers to the structure and behavior of the computer. It includes the specifications of the components, for example, instruction format, instruction set and techniques for addressing memory, and how they connect to the other components. Given the components,computer organization focuses on the organizational structure. It deals with how the hardware components operate and the way they are connected to form the computer. Given the system specifications, computer design focuses on the hardware to be used and the interconnection of parts. Different kinds of computer, such as a PC or a mainframe computer may have different organization; however, basic organization of the computer remains the same.
A computer consists of three main components—(1) Input/Output (I/O) Unit, (2) Central Processing Unit (CPU), and (3) Memory Unit. The computer user interacts with the computer via the I/O unit. The purpose of I/O unit is to provide data and instructions as input to the computer and to present relevant information as output from the computer. CPU controls the operations of the computer and processes the received input to generate the relevant output. The memory unit stores the instructions and the data during the input activity, to make instructions readily available to CPU during processing. It also stores the processed output. This chapter discusses the hardware components of the computer and the interaction between them.
Central Processing Unit
Central Processing Unit (CPU) or the processor is also often called the brain of computer. CPU (Figure 2.1) consists of Arithmetic Logic Unit (ALU) and Control Unit (CU). In addition, CPU also has a set of registers which are temporary storage areas for holding data, and instructions. ALU performs the arithmetic and logic operations on the data that is made available to it. CU is responsible for organizing the processing of data and instructions. CU controls and coordinates the activity of the other units of computer. CPU uses the registers to store the data, instructions during processing.
Figure 2.1. CPU

Memory Unit
The memory unit consists of cache memory and primary memory. Primary memory or main memory of the computer is used to store the data and instructions during execution of the instructions. Random Access Memory (RAM) and Read Only Memory (ROM) are the primary memory. In addition to the main memory, there is another kind of storage device known as the secondary memory. Secondary memory is non-volatile and is used for permanent storage of data and programs. A program or data that has to be executed is brought into the RAM from the secondary memory.
2.3.1. Cache Memory
• The data and instructions that are required during the processing of data are brought from the secondary storage devices and stored in the RAM. For processing, it is required that the data and instructions are accessed from the RAM and stored in the registers. The time taken to move the data between RAM and CPU registers is large. This affects the speed of processing of computer, and results in decreasing the performance of CPU.
• Cache memory is a very high speed memory placed in between RAM and CPU. Cache memory increases the speed of processing.
• Cache memory is a storage buffer that stores the data that is used more often, temporarily, and makes them available to CPU at a fast rate. During processing, CPU first checks cache for the required data. If data is not found in cache, then it looks in the RAM for data.
• To access the cache memory, CPU does not have to use the motherboard’s system bus for data transfer. (The data transfer speed slows to the motherboard’s capability, when data is passed through system bus. CPU can process data at a much faster rate by avoiding the system bus.)
• Cache memory is built into the processor, and may also be located next to it on a separate chip between the CPU and RAM. Cache built into the CPU is faster than separate cache, running at the speed of the microprocessor itself. However, separate cache is roughly twice as fast as RAM.
• The CPU has a built-in Level 1 (L1) cache and Level 2 (L2) cache, as shown inFigure 2.3. In addition to the built-in L1 and L2 cache, some CPUs have a separate cache chip on the motherboard. This cache on the motherboard is called Level 3 (L3)cache. Nowadays, high-end processor comes with built-in L3 cache, like in Intel core i7. The L1, L2 and L3 cache store the most recently run instructions, the next ones and the possible ones, respectively. Typically, CPUs have cache size varying from 256KB (L1), 6 MB (L2), to 12MB (L3) cache.
Figure 2.3. Illustration of cache memory

• Cache memory is very expensive, so it is smaller in size. Generally, computers have cache memory of sizes 256 KB to 2 MB.
Computer Cabinet
The computer cabinet encloses the components that are required for the running of the computer. The components inside a computer cabinet include the power supply, motherboard, memory chips, expansion slots, ports and interface, processor, cables and storage devices.
2.10.1. Motherboard
The computer is built up around a motherboard. The motherboard is the most important component in the PC. It is a large Printed Circuit Board (PCB), having many chips, connectors and other electronics mounted on it. The motherboard is the hub, which is used to connect all the essential components of a computer. The RAM, hard drive, disk drives and optical drives are all plugged into interfaces on the motherboard. The motherboard contains the processor, memory chips, interfaces and sockets, etc.
Memory Representation
The computer’s memory stores data, instructions required during the processing of data, and output results. Storage may be required for a limited period of time, instantly, or, for an extended period of time. Different types of memories, each having its own unique features, are available for use in a computer. The cache memory, registers, and RAM are fast memories and store the data and instructions temporarily during the processing of data and instructions. The secondary memory like magnetic disks and optical disks have large storage capacities and store the data and instructions permanently, but are slow memory devices. The memories are organized in the computer in a manner to achieve high levels of performance at the minimum cost.
Memory Representation
The computer memory stores different kinds of data like input data, output data, intermediate results, etc., and the instructions. Binary digit or bit is the basic unit of memory. A bit is a single binary digit, i.e., 0 or 1. A bit is the smallest unit of representation of data in a computer. However, the data is handled by the computer as a combination of bits. A group of 8 bits form a byte. One byte is the smallest unit of data that is handled by the computer. One byte can store 28, i.e., 256 different combinations of bits, and thus can be used to represent 256 different symbols. In a byte, the different combinations of bits fall in the range 00000000 to 11111111. A group of bytes can be further combined to form aword. A word can be a group of 2, 4 or 8 bytes.
1 bit = 0 or 1
1 Byte (B) = 8 bits
1 Kilobyte (KB) = 210 = 1024 bytes
1 Megabyte (MB) = 220 = 1024KB
1 Gigabyte (GB) = 230 = 1024 MB = 1024 *1024 KB
1 Terabyte (TB) = 240= 1024 GB = 1024 * 1024 *1024 KB
Primary Memory
Primary memory is the main memory of computer. It is a chip mounted on the motherboard of computer. Primary memory is categorized into two main types-
• Random Access Memory (RAM), and
• Read Only Memory (ROM)
Secondary Memory
In the previous section, we saw that RAM is expensive and has a limited storage capacity. Since it is a volatile memory, it cannot retain information after the computer is powered off. Thus, in addition to primary memory, an auxiliary or secondary memory is required by a computer. The secondary memory is also called the storage device of computer. In this chapter, the terms secondary memory and storage device are used interchangeably. In comparison to the primary memory, the secondary memory stores much larger amounts of data and information (for example, an entire software program) for extended periods of time. The data and instructions stored in secondary memory must be fetched into RAM before processing is done by CPU.
Magnetic tape drives, magnetic disk drives, optical disk drives and magneto-optical disk drives are the different types of storage devices.
Access Types of Storage Devices
 Magnetic Tape
Magnetic tape is a plastic tape with magnetic coating (Figure 3.7). It is a storage medium on a large open reel or in a smaller cartridge or cassette (like a music cassette). Magnetic tapes are cheaper storage media. They are durable, can be written, erased, and re-written. Magnetic tapes are sequential access devices, which mean that the tape needs to rewind or move forward to the location where the requested data is positioned in the magnetic tape. Due to their sequential nature, magnetic tapes are not suitable for data files that need to be revised or updated often. They are generally used to store back-up data that is not frequently used or to transfer data from one system to other.
Figure 3.7. A 10.5-inch reel of 9-track tape

Optical Disk
Optical disk (Figure 3.14) is a flat and circular disk which is coated with reflective plastic material that can be altered by laser light. Optical disk does not use magnetism. The bits 1 and 0 are stored as spots that are relatively bright and light, respectively.
Figure 3.14. Optical disk


Using the Computer Memory
The computer starts using the memory from the moment the computer is switched on, till the time it is switched off. The list of steps that the computer performs from the time it is switched on are—
• Turn the computer on.
• The computer loads data from ROM. It makes sure that all the major components of the computer are functioning properly.
• The computer loads the BIOS from ROM. The BIOS provides the most basic information about storage devices, boot sequence, security, plug and play capability and other items.
• The computer loads the OS from the hard drive into the system’s RAM. CPU has immediate access to the OS as the critical parts of the OS are maintained in RAM as long as the computer is on. This enhances the performance and functionality of the overall system.
• Now the system is ready for use.
• When you load or open an application it is loaded in the RAM. Since the CPU looks for information in the RAM, any data and instructions that are required for processing (read, write or update) is brought into RAM. To conserve RAM usage, many applications load only the essential parts of the program initially and then load other pieces as needed. Any files that are opened for use in that application are also loaded into RAM.
• The CPU requests the data it needs from RAM, processes it and writes new data back to RAM in a continuous cycle. The shuffling of data between the CPU and RAM happens millions of times every second.
• When you save a file and close the application, the file is written to the secondary memory as specified by you. The application and any accompanying files usually get deleted from RAM to make space for new data.
• If the files are not saved to a storage device before being closed, they are lost.
Introduction
A computer interacts with the external environment via the input-output (I/O) devices attached to it. Input device is used for providing data and instructions to the computer. After processing the input data, computer provides output to the user via the output device. The I/O devices that are attached, externally, to the computer machine are also called peripheral devices. Different kinds of input and output devices are used for different kinds of input and output requirements. In this chapter, we shall discuss different kinds of input devices and output devices.

Input-Output Unit
An I/O unit is a component of computer. The I/O unit is composed of two parts—input unit and output unit. The input unit is responsible for providing input to the computer and the output unit is for receiving output from the computer.
4.2.1. Input Unit
• The input unit gets the data and programs from various input devices and makes them available for processing to other units of the computer.
• The input data is provided through input devices, such as—keyboard, mouse, trackball and joystick. Input data can also be provided by scanning images, voice recording, video recording, etc.
• Irrespective of the kind of input data provided to a computer, all input devices must translate the input data into a form that is understandable by the computer, i.e., in machine readable form. The transformation of the input data to machine readable form is done by the input interface of input device.
Input Devices
Input devices allow users and other applications to input data into the computer, for processing. The data input to a computer can be in the form of text, audio, video, etc.Figure 4.1 shows some users working in an office. The data is entered manually by the user or with minimal user intervention. Input devices are classified as follows—



Human Data Entry Devices
Input devices that require data to be entered manually to the computer are identified as human data entry devices. The data may be entered by typing or keying in, or by pointing a device to a particular location.
4.4.1. Keyboard
Features Keyboard is a common input device. It is provided along with the computer, and is easy to use. It is used for entering the text data. For inputting the data, the user types the data using the keyboard. When the data is being typed, the display monitor displays the typed data. Cursor is a vertical line, an underscore, blinking line, etc. Cursor moves with each typed character. The position of cursor indicates the location on monitor where the typed-in character will be displayed.
 Output Devices
Output devices provide output to the user, which is generated after processing the input data. The processed data, presented to the user via the output devices could be text, graphics, audio or video. The output could be on a paper or on a film in a tangible form, or, in an intangible form as audio, video and electronic form. Output devices are classified as follows—
• Hard Copy Devices
o Printer
o Plotter
• Soft Copy Devices
o Monitor
o Video Output
o Audio Response
 I/O Port
The peripheral devices can be connected to computer in several ways. Devices such as network adapters and sound cards are connected to expansion slots inside the computer. Printers and scanners are connected to ports on the backside of the computer. Also in a portable computer, the PC Card connects to the PC Card slot on it.
The I/O ports are the external interfaces that are used to connect input and output devices like printer, modem and joystick to the computer. The I/O devices are connected to the computer via the serial and parallel ports, Universal Serial Bus (USB) port, Firewire port, etc.
Introduction
The data stored in the computer may be of different kinds, as follows—
• Numeric data (0, 1, 2, ..., 9)
• Alphabetic data (A, B, C, ..., Z)
• Alphanumeric data—Combination of any of the symbols—(A, B, C... Z), (0, 1... 9), or special characters (+,–, Blank), etc.
• User-Computer Interface
• Interaction of User and Computer
Contents
• Types of software—System software, and application software
• System software
o For management and functionality of computer—Operating system, device drivers, and system utilities
o For development of application software—Programming languages, translator software, loader, and linker
• Operating system
• Device drivers
• System utility software—Anti-virus, data compression, cryptographic, disk compression, disk partitioning, disk cleaner, backup, system profiling, and network manager
• Programming language—Machine language, assembly language, high-level language, and different generations of programming languages
• Linker, and loader software
• Application software—Word processing software, image processing software, accounting software, spreadsheet software, presentation software, and web browser software
Operating System
Contents
• Objectives of OS
• Types of OS—Single user and single task, single user and multitasking, multiuser, multiprocessing, real time, embedded OS
• Functions of OS—Process management, memory management, file management, device management, protection and security, user interface
• Process management
o Process—Process states (new, ready, running, waiting, terminated)
o CPU scheduling—Scheduler, scheduling algorithms (FCFS, SJF, RR)
o Process synchronization—Concurrent processes, race condition
o Deadlock—Deadlock conditions, deadlock prevention, deadlock avoidance
• Memory management
o Memory allocation—Multiple partition allocation, paging
o Virtual memory—Demand paging
• File management—Files, directory structure
• Device management—Device drivers, I/O scheduling, buffering, spooling
• Protection and security
• User interface—CLI, GUI
• Examples of operating systems—MS-DOS, Windows family of OS, Linux
Types of Software
Software can be broadly classified in two categories:
1. System Software, and
2. Application Software.
System Software
System software provides basic functionality to the computer. System software is required for the working of computer itself. The user of computer does not need to be aware about the functioning of system software, while using the computer. For example, when you buy a computer, the system software would also include different device drivers. When you request for using any of the devices, the corresponding device driver software interacts with the hardware device to perform the specified request. If the appropriate device driver for any device, say a particular model of a printer, is installed on the computer, the user does not need to know about the device driver, while printing on this printer.
The purposes of the system software are:
Application Software
The software that a user uses for accomplishing a specific task is the application software. Application software may be a single program or a set of programs. A set of programs that are written for a specific purpose and provide the required functionality is called software package. Application software is written for different kinds of applications—graphics, word processors, media players, database applications, telecommunication, accounting purposes etc.
Summary
• Software can be classified into two categories—System Software, and Application Software.
• System software provides basic functionality to the computer, controls computer hardware, and acts as an interface between user and computer hardware. System software may be used for the management of the computer, and, for the development of application software.
• Operating System (OS) intermediates between user of computer and computer hardware. It manages resources of the computer system, controls execution of programs, and provides a convenient interface to the user for use of the computer.
• MS-DOS, Windows XP, Windows 7, UNIX and Mac OS X, are some examples of OS.
• Device driver intermediates between the device and the software that uses the device. Each device has its own device driver, which must be installed on the computer for the proper working of the device. Device drivers can be character orblock device drivers.
• For plug and play devices, the device drivers come preloaded with the operating system.
• System utility software is required for maintenance of the computer. Anti-virus, data compression, disk partitioning, backup, system profiling are some system utilities.
• Programming languages include a set of commands that the user follows to write a program.
• Machine language is defined by the hardware of the computer. A program written in machine language is very fast, machine-dependent, and is difficult to write.
• Assembly language uses symbolic representation of machine code. An assembly language program is easier to write than the machine language program but is still machine dependent.
• A program written in a high-level language is English-like. High-level language programs are easier to write and are easily portable from one computer to another.
• The programming languages are classified into five generation of languages.
• Translator software is used to convert a program written in high-level language and assembly language to a form that the computer can understand. Assembler, compiler, and interpreter are the three kinds of translator software.
• Assembler converts a program written in assembly language into machine code.
• Compiler translates the program written in a high-level language to machine language. The high-level language program is the source code, and compiled program is the object code.
• Interpreter converts the high-level language program into machine code, but performs line-by-line execution of the source code, during the program execution.
• Linker links several object modules and libraries to a single executable program.
• Loader loads and re-locates the executable program in the main memory.
• Application software is a single program or a set of programs that perform a specific task. Word processing software, image processing software, geographical information systems, accounting software, spreadsheet, presentation software, and web browser software are examples of application software.
• Software acquisition may require the user to purchase the software like retail software, or use free software like freeware, public-domain software, and open-source software.
Questions
Section 6.1–6.3
1. _____ and _____ are the two main categories of software.
2. What is the purpose of system software?
3. What is system software?
4. Give two examples of system software.
5. Describe the two categories of system software.
Section 6.3.1–6.3.3
6. What is the need of an operating system?
7. Describe the functions of an operating system.
8. “OS controls and coordinates the use of hardware among the different application software and the users”. Explain.
9. Name any three operating systems.
10. Define a device driver.
11. What are plug and play devices?
12. Give an example of a plug and play device.
13. Where is the device driver of the plug and play device located on the computer?
14. What is the purpose of a device driver?
15. What are character device driver and block device driver?
16. Give an example of a character device driver.
17. Give an example of a block device driver.
18. What are the uses of system utilities?
19. List any five system utilities and also list the purpose of each.
20. Explain the purpose of the following system utilities in one line—(i) Anti-virus, (ii) Data compression, (iii) Cryptographic, (iv) Disk compression, (v) Disk partitioning, (vi) Disk cleaners, (vii) Backup utility, (viii) System Profiling utility, (ix) Network managers.
7.1. Introduction
The computer system comprises of a functional set of hardware, software, user and data. Hardware consists of the components of computer like memory, processor, storage devices, and Input/Output devices. The software may be of different kinds—application software and system software. A computer system may be a single stand-alone system or may consist of several interconnected systems. The user uses the application software to perform various tasks, for example, the user uses word processing software for document preparation. While using the application software, the user uses the storage of a computer—to store a document on the hard disk, to execute a command on the CPU, to retrieve a document from a peripheral device or to print document on printer. For using the hardware, there is a need for software that interacts with both the hardware and the application software. Operating system (OS) is the software that provides an interface between the computer hardware, and the application programs or users (Figure 7.1).
Figure 7.1. View of components of computer system



Types of OS
OS are classified into different types depending on their capability of processing—(1) Single user, (2) Multiuser, (3) Multitasking, (4) Multiprocessing, (5) Real time, and (6) Embedded.
• Single User and Single Task OS is for use by a single user for a standalone single computer for performing a single task (Figure 7.2). Operating system for Personal Computers (PC) are single-user OS. For example, if the user is editing a document, then a document cannot be printed on the printer simultaneously. Single user OS are simple operating system designed to manage one task at a time. MS-DOS is an example of single user OS.
Figure 7.2. A single user performing a single task

• Single User and Multitasking OS allows execution of more than one task or process concurrently. For this, the processor time is divided amongst different tasks. This division of time is also called time sharing. The processor switches rapidly between processes. For example, the user can listen to music on the computer while writing an article using a word processor software. The user can switch between the applications and also transfer data between them (Figure 7.3). Windows 95 and all later versions of Windows are examples of multitasking OS.
Figure 7.3. A single user performing multitasking (issuing print command and making drawings)

• Multiuser OS is used in computer networks that allow same data and applications to be accessed by multiple users at the same time (Figure 7.4). The users can also communicate with each other. Linux, UNIX, and Windows 7 are examples of multiuser OS.
Figure 7.4. Multiple users working on connected computers

• Multiprocessing OS have two or more processors for a single running process. Processing takes place in parallel and is also called parallel processing. Each processor works on different parts of the same task, or, on two or more different tasks. Since execution takes place in parallel, they are used for high speed execution, and to increase the power of computer. Linux, UNIX and Windows 7 are examples of multiprocessing OS.
• Embedded OS is embedded in a device in the ROM. They are specific to a device and are less resource intensive. They are used in appliances like microwaves, washing machines, traffic control systems etc.
Functions of OS
Operating system is a large and complex software consisting of several components. Each component of the operating system has its own set of defined inputs and outputs. Different components of OS perform specific tasks to provide the overall functionality of the operating system (Figure 7.5). Main functions of the operating system are as follows:
• Process Management— The process management activities handled by the OS are—(1) control access to shared resources like file, memory, I/O and CPU, (2) control execution of applications, (3) create, execute and delete a process (system process or user process), (4) cancel or resume a process (5) schedule a process, and (6) synchronization, communication and deadlock handling for processes.
Figure 7.5. Functions of OS

• Memory Management— The activities of memory management handled by OS are—(1) allocate memory, (2) free memory, (3) re-allocate memory to a program when a used block is freed, and (4) keep track of memory usage.
• File Management— The file management tasks include—(1) create and delete both files and directories, (2) provide access to files, (3) allocate space for files, (4) keep back-up of files, and (5) secure files.
• Device Management— The device management tasks handled by OS are—(1) open, close and write device drivers, and (2) communicate, control and monitor the device driver.
• Protection and Security— OS protects the resources of system. User authentication, file attributes like read, write, and back-up of data are used by OS to provide basic protection.
• User Interface or Command Interpreter— Operating system provides an interface between the computer user and the computer hardware. The user interface is a set of commands or a graphical user interface via which the user interacts with the applications and the hardware.


Process Management
• A process is a program in a state of execution. It is a unit of work for the operating system. A process can be created, executed, and stopped. In contrast, a program is always static and does not have any state. A program may have two or more processes running. A process and a program are, thus, two different entities.
• To accomplish a task, a process needs to have access to different system resources like I/O devices, CPU, memory etc. The process management function of an operating system handles allocation of resources to the processes in an efficient manner. The allocation of resources required by a process is made during process creation and process execution.
• A process changes its state as it is executed. The various states that a process changes during execution are as follows (Figure 7.6):
Figure 7.6. Process states


o New—process is in a new state when it is created,
o Ready—process is in ready state when it is waiting for a processor,
o Running—process is in running state if processor is executing the process,
o Waiting—process is in waiting state when it waits for some event to happen (I/O etc), and
o Terminated—process that has finished execution is in terminated state.
• A system consists of collection of processes—(1) system process that execute system code, and (2) user process that execute user code. OS mainly handles the execution of user code, though it may also handle various system processes.
Memory Management
In a computer, there may be multiple processes executing at the same time. Every process that needs to execute, requires a certain amount of memory. Memory management is one of the tasks handled by the operating system. Memory management schemes handle the allocation of memory to different processes. On completion of process execution, the memory is de-allocated and made available to another process. Additionally, different processes that have been allocated memory should not interfere into each other’s memory space. This requires some memory protection and sharing mechanism. Now we will discuss memory allocation, de-allocation, re-allocation of free memory, and memory protection and sharing.
Memory Allocation
• In single-user and single-task operating system like MS-DOS, only one process can execute at a time. After the termination of the process, the allocated memory is freed and is made available to any other process.
• In a multiprogramming system, in addition to allocation and de-allocation of memory, more tasks are involved like keeping track of processes allocated to the memory, memory protection and sharing etc.
• There are different memory allocation schemes to allocate memory to the processes that reside in memory at the same time. The different memory allocation schemes are as follows:
o Multiple Partition Allocation— The operating system keeps track of blocks of memory which are free and those which are unavailable. The single block of available memory is called a hole. When a process requires memory, a hole large enough for the process is allocated. As different processes release the memory, the released block of memory is placed in the set of holes. During allocation of memory, the set of holes is searched to determine which hole is to be allocated. For this, three hole allocation strategies are used—(1) first-fit (allocate the first hole that is big enough for the process, (2) best-fit (allocate the smallest hole that is big enough for the process, and (3) worst-fit (allocate the largest available hole). Memory allocated using any of these strategies results in fragmentation. When the processes are allocated memory and removed from memory, the free memory is broken into small pieces. These small pieces of fragmented memory lie unused. Paging scheme is used to overcome fragmentation. Figure 7.9 shows allocation of memory to a process requiring 8 KB of memory, using the first fit, best fit, and worst fit allocation strategies.
Figure 7.9. Multiple partition memory allocation



File Management
• The file management function of the operating system involves handling the file system which consists of two parts—a set of files, and a directory structure.
• File is a collection of related information, has a name, and is stored on a secondary storage. It is the smallest named unit that can be written to a secondary storage device. Data cannot be stored on the secondary storage if it is not in the form of a file. A file has attributes like its name, location, size, type, time, and date of creation etc. (Figure 7.12). The information stored in a file can be accessed in different ways—sequential access (access is in a sequential order from start to end) and direct access (the file can be accessed in any order).
Figure 7.12. Showing the file attributes
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• Directory structure provides information about the files stored on the secondary storage. Directory contains information about all the files within it. The information about the files is kept as entries in the directory of device. A directory further may have a sub-directory defined within it. Directory contains the name, location, size, and type of all the files defined on the device. The tree-structured directory (Figure 7.13) is the commonly used directory structure.
Figure 7.13. Tree-structured directory in Windows XP



• The operating system manages the storage media like the disk and implements the abstract concept of the file. System calls are an interface between the process and the operating system. Operating system provides system calls for creating, reading, writing, deleting, repositioning, and truncating a file. Some of the operations that can be performed on a directory are—search for a file, create, delete and rename a file, list a directory, and traverse the file system within the directory. The user simply uses the system calls like “dir”, “list” to perform operation on a file or directory, without going into the details of its working.

Device Management
• Several peripheral devices like mouse, hard disk, printer, plotter etc. are connected to the computer. The peripheral devices have varying characteristics like character or block device, sequential or random access device, and dedicated or shared device.
• OS manages and controls the devices attached to the computer. OS provides appropriate functionality to the application programs for controlling different aspects of the devices. Figure 7.14 shows the device manager and system properties in Windows XP Professional.
Figure 7.14. Device manager and system properties in Windows XP Professional

• OS handles the devices by combining both hardware and software techniques. The I/O hardware includes the ports, buses, and device controllers for the devices. The OS communicates with the I/O hardware via the device driver software. The device driver software comes along with each device.
• A device communicates with the computer hardware via a port (for example, a serial port or a parallel port). Bus is a common set of wires used by one or more devices. The computer uses different kinds of buses like PCI bus for connecting processor or memory to the fast devices, expansion bus to connect to slow I/O devices and SCSI bus to connect disks. A device controller operates a port, bus, and a device. Device controller is just like a bridge between the device and the operating system. The device controller receives the data from a connected device, stores it temporarily, and then communicates the data to the device’s device driver. Device driver is the software with which the device controller communicates with the operating system (Figure 7.15).
Figure 7.15. Devices interacting with OS


Protection and Security
• The access of programs, processes, and users, to the resources defined by the computer are controlled by the protection mechanism.
• Protection ensures that the resources of the computer are used in a consistent way.
• Security mechanism prevents unauthorized access to the computer. Security concerns include—security of software, security of data stored in the computer, and security of physical resources of the computer.
• In a personal computer, security can be ensured using—(1) user accounts—individual accounts for each user, (2) user authentication—using password protection (Figure 7.16), (3) access rights—define rights for access of different kind of information for different people, (4) data encryption—store data in computer in encrypted form, and (5) data backup—storing data on a peripheral device other than the hard disk. In a networked environment, only trusted computers should be able to share data. Some of the common security threats occur due to hacking, viruses etc.
Figure 7.16. Create password and manage user account in Windows XP Professional
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User Interface
• The primary goal of operating system is to make the computer convenient for use by its user. It should allow users to easily access and communicate with the applications and the hardware.
• The users can interact with the computer by using mainly two kinds of interfaces—(1) Command Line Interface (CLI), and (2) Graphical User Interface (GUI).
• CLI requires the user to interact with operating system in the form of text keyed in from the keyboard. In this, the user has to learn and remember the different commands required for copying, deleting, opening a file or folder etc. (Figure 7.17). MS-DOS and Linux shell are examples of command line mode of interfaces.
Figure 7.17. Command line interface
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• GUI use graphics to display the various commands. The interface consists of icons, menus, windows, and pointers. The user need not learn the commands, instead, the user can give instructions by moving the pointer on the screen using a mouse and pressing the mouse button (Figure 7.18). “Windows 7” and “Mac OS 10” are examples of graphical mode of interface. GUI interface for the Linux OS also exist like the GNU Object Model Environment (GNOME).
Figure 7.18. Graphical user interface
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Examples of Operating Systems
MS-DOS, Windows family of operating systems, Unix OS, Linux OS, and Mac OS X are some of examples of commonly used OSs. Each operating system has specific characteristics. Here, we will discuss the features of the MS-DOS, Windows family of operating systems and Linux operating system.
7.11.1. MS-DOS
• MS-DOS was the first widely-installed operating system for PCs in 1980s.
• MS-DOS is easy to load and install. It neither requires much memory for the operating system, nor a very powerful computer to run on.
• MS-DOS is a command line user interface operating system. This means that the user has to type single line commands through the command interface. So, user has to remember the different commands and their syntax.
• It is a single-user and single-tasking operating system for the PC. Only one user can use it and only one task can be executed, at a given point of time. Also, it does not have a built-in support for networking.
• MS-DOS is a 16-bit OS, meaning thereby that it can send or receive 16 bits of data at a time and can process 16 bits of data. It is not able to take the advantage of 32-bit processors.
• To use MS-DOS, user must know where the programs and data are stored and how to interact with it. In the MS-DOS command mode, command.com routine interprets the typed in command from the keyboard.
Summary
• Operating system intermediates between the computer hardware and the computer user.
• The objective of OS is to make the computer system convenient for the user to use, and to use the computer hardware efficiently.
• Types of OS—Single user and single task OS is for use by a single user for a single task. Multitasking OS allow execution of more than one task concurrently. Multiuser OS allows concurrent access of same data and applications by multiple users. Multiprocessing OS have two or more processors for a single running process, which execute in parallel. Real time OS respond to an event within a predetermined time. Embedded OS is embedded in appliances like microwaves and washing machines.
• Functions of OS are process management, memory management, file management, device management, protection and security, and user interface.
• Process management includes handling the scheduling of processes, process synchronization and communication, and deadlock situations.
• A process is a program in a state of execution. During execution, a process can be in a new, ready, running, waiting or terminated state.
• CPU scheduler assigns the processor to different processes so that no process is kept waiting for long. Scheduling can be non-pre-emptive scheduling and pre-emptive scheduling.
• FCFS, SJF and RR are CPU scheduling algorithms. In FCFS, process that requests for CPU first gets the CPU first. In SJF, process that requires least CPU time, is allocated the CPU first. In RR scheduling, each process in the queue gets CPU for a quantum of time circularly.
• Process synchronization is required when multiple processes access and manipulate the same data, concurrently.
• A deadlock arises when the four necessary conditions—mutual exclusion, no preemption, hold and wait, and circular wait, hold true simultaneously in a system.
• Memory management includes memory allocation, de-allocation, re-allocation of free block, and memory protection and sharing.
• The file manager handles the file system consisting of a set of files and a directory structure. OS provides system calls for performing operations on the file.
• OS handles the devices using a combination of hardware and software techniques. The I/O hardware includes the ports, buses and device controllers for the devices. OS interacts with I/O hardware via the device driver software of the device.
• Protection ensures that the resources of computer are used in a consistent way.Security mechanism prevents unauthorized access to a system.
• CUI and GUI are the two kinds of user interfaces.
• MS-DOS, Windows XP, UNIX, Linux, and Mac OS X are some examples of OSs.
Computer Network
Introduction
The communication process involves—sender of information, receiver of information, language used for communication, and medium used to establish the communication. Communication between computers also follows a similar process.
This chapter discusses the data communication and the computer networks. The section on data communication discusses the media used for transmission of data, how data can be transferred across the communication media and the relationship between data transmission and data networking. The section on computer network discusses different network types, network topologies, communication protocol and network communicating devices. A brief explanation of wireless networks is also provided.
Importance of Networking
Networking of computers provides a communication link between the users, and provides access to information. Networking of computers has several uses, described as follows:
• Resource Sharing— In an organization, resources such as printers, fax machines and scanners are generally not required by each person at all times. Moreover, for small organizations it may not be feasible to provide such resources to each individual. Such resources can be made available to different users of the organization on the network. It results in availability of the resource to different users regardless of the physical location of the resource or the user, enhances optimal use of the resource, leads to easy maintenance, and saves cost too (Figure 9.1).
Figure 9.1. A network of computers, printer and scanner

• Sharing of Information— In addition to the sharing of physical resources, networking facilitates sharing of information. Information stored on networked computers located at same or different physical locations, becomes accessible to the computers connected to the network.
• As a Communication Medium— Networking helps in sending and receiving of electronic-mail (e-mail) messages from anywhere in the world. Data in the form of text, audio, video and pictures can be sent via e-mail. This allows the users to communicate online in a faster and cost effective manner. Video conferencing is another form of communication made possible via networking. People in distant locations can hold a meeting, and they can hear and see each other simultaneously.
• For Back-up and Support— Networked computers can be used to take back-up of critical data. In situations where there is a requirement of always-on computer, another computer on the network can take over in case of failure of one computer.
Data Transmission Media
The data is sent from one computer to another over a transmission medium. The transmission media can be grouped into guided media, and unguided media.
In the guided media, the data signals are sent along a specific path, through a wire or a cable. Copper wire and optical fibers are the most commonly used guided media. Copper wire transmits data as electric signals. Copper wires offer low resistance to current signal, facilitating signals to travel longer distances. To minimize the effect of external disturbance on the copper wire, two types of wiring is used—(1) Twisted Pair, and (2) Coaxial Pair. Optical fibers transmit data as light signals.
Computer Network
A computer network is an interconnection of two or more computers that are able to exchange information. The computers may be connected via any data communication link, like copper wires, optical fibers, communication satellites, or radio links. The computers connected to the network may be personal computers or large main frames. The computers in a network may be located in a room, building, city, country, or anywhere in the world.
9.6.1. Network Types
Computer network is broadly classified into three types—(1) Local Area Network (LAN), (2)Metropolitan Area Network (MAN), and (3) Wide Area Network (WAN). The different network types are distinguished from each other based on the following characteristics:
Wireless Networking
Wireless technology, as the name suggests, is used to establish a wire-free connection or communication between two or more devices. In contrast to the wired technology where data is encoded as electric current and signals travel through wires, in wireless technology data is encoded on electromagnetic waves that travel through air. The wireless technology is used for broadcasting in radio and television communication, for communication using mobile phones and pagers, for connecting components of computers using Bluetooth technology, for Internet connection using Wi-Fi, Wireless LAN, PDA, and in remote controls for television, doors etc.
• Wireless network is a computer network connected wirelessly. The communication is done through a wireless media like radio waves, infrared or Bluetooth.
• The wireless networks have two main components—the wireless access points that include the transmitter along with the area it can cover, and the wireless clients like mobile handsets, laptops with Ethernet cards etc.
• The access point receives data frames from the computers attached to it wirelessly, checks the frames, and transmits them to their destination. The coverage area of a transmitter depends on the output power of the transmitter, its location, and the frequency used to transmit the data. Higher frequencies require a clear line of sight as compared to lower frequencies.
• The speed of wireless connection is determined by the distance of the wireless client device from the access point, the obstruction-free path (walls, trees etc.), interference, and the number of users using the network at a given time.
• Wireless networks can be divided into three categories based on their use:
o Bluetooth technology to connect the different components of the computer in a room, a small office or home.
o Wireless LAN is used to connect computers and devices wirelessly in a LAN, for example, different computers or devices in an office or campus.
o Wireless WAN is used to connect wide area systems, for example access to Internet via mobile devices like cell phone, PDAs and laptops.
The Internet and Internet Services
Contents
• History of Internet—TCP/IP, Internet applications, WWW, browser
• Internetworking protocol—TCP/IP
• Internet architecture—Client, local ISP, regional ISP, backbone
• Connecting to Internet
• Internet connections—Dial-up access, leased line, cable modem
• Internet address
• Internet services
o WWW—Web browser, URL, Internet search engines, WWW development languages
o Electronic mail—E-mail address, e-mail message format, e-mail services (application based e-mail, webmail), how email works (client-server model)
o File transfer protocol—How FTP works (client-server model)
o Terminal network
o News
o Internet relay chat

Introduction
In the previous chapter, we discussed about the computer networks. The computers interconnected by LAN, MAN, and WAN are able to exchange information, within their networks, i.e. a computer connected to one network is able to exchange information with another computer connected to the same network. However, a computer connected to a particular network may need to interact with a computer connected to a different network.
Internet is defined as an interconnection of networks. Internet allows computers on different kinds of networks to interact with each other. Any two computers, often having different software and hardware, can exchange information over the Internet, as long as they obey the technical rules of Internet communication. The exchange of information may be among connected computers located anywhere, like military and research institutions, different kinds of organizations, banks, educational institutions (elementary schools, high schools, colleges), public libraries, commercial sectors etc.

Internetworking Protocol
• TCP/IP is the communication protocol for the Internet.
• The TCP/IP protocol has two parts: TCP and IP.
• Transmission Control Protocol (TCP) provides reliable transport service, i.e. it ensures that messages sent from sender to receiver are properly routed and arrive intact at the destination.
• TCP converts messages into a set of packets at the source, which are then reassembled back into messages at the destination. For this, TCP operates with thepacket switching technique, which is described as follows:
o The message is divided into small packets.
o Each packet contains address, sequencing information, and error control information.
o The address is used to route the packet to its destination.
o Since multiple users can send or receive information over the same communication line, the packets can arrive out of order at the destination. The sequencing information in the packet is used to reassemble the packets in order, at their destination.
o The error control information is used to check that the packet arrived at the destination is the same as that sent from the source (i.e. has not got corrupted)
• Internet Protocol (IP) allows different computers to communicate by creating a network of networks.
• IP handles the dispatch of packets over the network.
• It handles the addressing of packets,
The computers connected to Internet may be personal computers or mainframes; the computers could have a slow or fast CPU, small or large memory, connected to different networks having slow or fast speed. TCP/IP protocol makes it possible for any pair of computers connected to Internet to communicate, despite their hardware differences.


The Internet Architecture
Internet is a network of interconnected networks and is designed to operate without a central control. If a portion of the network fails, connection is made through alternative paths available. The architecture of Internet is hierarchical in nature. A brief description of the architecture of Internet is as follows:
• Client (user of computer) at home or in a LAN network is at the lowest level in hierarchy.
• Local Internet Service Provider (ISP) is at the next higher level.
o An ISP is an organization that has its own computers connected to the Internet and provides facility to individual users to connect to Internet through their computers.
o Local ISP is the local telephone company located in the telephone switching office, where the telephone of client terminates. Examples of local ISP in India are Bharat Sanchar Nigam Ltd. (BSNL), Mahanagar Telephone Nigam Ltd. (MTNL), and Airtel.
o The client calls local ISP using a modem or Network Interface Card.

Connecting to Internet
To be able to connect your computer to the Internet, you require—(1) a TCP/IP enabled computer, (2) web browser software, (3) an account with an ISP, (4) a telephone line, and (5) a modem or Network Interface Card (NIC) to connect the telephone line to the computer (Figure 10.2).
Figure 10.2. Connecting to Internet
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Internet Address
A computer connected to the Internet must have a unique address in order to communicate across the Internet. Internet Protocol (IP) address is assigned uniquely to every computer connected to the Internet. IP address is provided by the ISP whose services you use to connect your computer to the Internet. IP address is a string of numbers consisting of four parts, where each part is a number between 0 and 255. An IP address looks like 201.54.122.107. Since IP addresses are numeric, it is difficult to remember everyone’s IP address. So, instead of numeric IP address, domain name is used.
Internet Services
Internet is a huge de-centralized network that connects computers. Every computer connected to the Internet has a unique address, which helps to identify the computer on the Internet uniquely. Over the years, Internet has grown as the biggest network for communication and provides several services to its users. Each service has its own features and uses. Some of the important services provided by Internet are—World Wide Web, electronic mail, news, chat, and discussion groups.
10.9.1. World Wide Web (WWW)
WWW (also called as Web) is a large scale, online store of information. It is a system of creating, organizing, and linking of documents. Information is stored on WWW as a collection of documents that are interconnected with each other via links. The interconnected documents may be located on one or more than one computer, worldwide, thus, the name world wide web. The features of WWW and terms linked to WWW are given below—
Uses of Internet
Internet is used for different purposes by different people. Some uses of the Internet (Figure 10.17) are listed below:
• E-Commerce (auction, buying, selling products etc.)
• Research (on-line journals, magazines, information etc.)
• Education (e-learning courses, virtual classroom, distance learning)
• E-Governance (online filing of application (Income Tax), on-line application forms etc.)
• On-line ticket booking (airplane tickets, rail tickets, cinema hall tickets etc.)
• On-line payments (credit card payments etc.)
• Video conferencing
• Exchange of views, music, files, mails, folders, data, information etc.
• Social networking (sites like facebook, linkedin, twitter, orkut)
• E-Telephony (sites like skype)


Database
Database is a repository or collection of logically related, and similar data. Database stores similar kind of data that is organized in a manner that the information can be derived from it, modified, data added, or deleted to it, and used when needed. Some examples of databases in real life situations are: dictionary—a database of words organized alphabetically along with their meaning, telephone directory—a database of telephone numbers and addresses organized by the last name of people, railway timetable—a database of trains organized by train names, and, companies listed on Stock Exchange organized by names alphabetically.
A database is defined as—(1) a collection, or repository of data, (2) having an organized structure, and (3) for a specific purpose. A database stores information, which is useful to an organization. It contains data based on the kind of application for which it is required. For example, an airline database may contain data about the airplane, the routes, airline reservation, airline schedules etc.; a college database may contain data about the students, faculty, administrative staff, courses, results etc.; a database for manufacturing application may contain data about the production, inventory, supply chain, orders, sales etc.; and a student database may contain data about students, like student names, student course etc.
Database System
A bank, hospital, college, university, manufacturer, government are some examples of organizations or enterprises that are established for specific purposes. All organizations or enterprises have some basic common functions. They need to collect and store data, process data, and disseminate data for their various functions depending on the kind of organization. Some of the common functions include payroll, sales report etc.
A database system integrates the collection, storage, and dissemination of data required for the different operations of an organization, under a single administration. A database system is a computerized record keeping system. The purpose of the database system is to maintain the data and to make the information available on demand.
Database Management System
The interrelated set of data that forms the database needs to be stored and managed, so that the database can be accessed for the retrieval of data, and for insertion, deletion, or updating of data. DBMS is a software system for creating, organizing and managing the database. DBMS handles all access to the database and manages the database. Managing the database implies that it provides a convenient environment to the user to perform operations on the database for creation, insertion, deletion, updating, and retrieval of data. DBMS defines the scope of the use of database. This keeps data secure from unauthorized access. The functionality of DBMS includes—(1) the database that contains interrelated data, and (2) a set of programs to access the data. The DBMS implements the three schema architecture—internal schema at internal level, conceptual schema at conceptual level, and external schema at external level. The different DBMSs may not provide a clean distinction between the three levels, but generally they follow the three schema architecture.

12.5.1. Centralized DBMS Architecture
• Centralized databases are the traditional database systems where all database functionality, data, application program and user interface processing are located on one machine. Access to the database from remote locations is via the communication links (Figure 12.11).
Figure 12.11. Centralized database

• In the early systems, the mainframe computers provided all the functionality required by the users of computer. The users interacted with the mainframe computers via dumb terminals. All processing was performed on the mainframe computer. The DBMS was centralized, and stored on the mainframes. The dumb terminals had only the display facility.
• The centralized database is easy to manage and administer.
• Common examples of centralized databases are personal database, and central computer database.

Multimedia
Contents
• Multimedia: definition—Mass media and multimedia
• Characteristics of multimedia system—Computer, integration of elements, digital format, interactive
• Elements of multimedia
o Text—Text font, text effects, text animation, text on the Internet
o Graphics—Image resolution, image color, image file size, image compression, image capture, bitmap graphics, vector graphics
o Audio—Properties of sound, digital audio, sound hardware, sound sampling, sound digitization, music and speech, audio file formats, audio editors, sound compression, selecting a quality audio, audio from a CD to web
o Video—Analog and digital video, video editing, digitizing analog video, video compression, video file formats, video on Internet
o Animation—Process of animation, creation of animation, hardware and software for animation, animation file formats
• Multimedia system—Desirable features of multimedia system
• Multimedia applications—Education, entertainment, training, business, virtual reality

Introduction
Newspaper and television are the common medium of mass communication. However, they differ in the way they present information to the user. The information in a newspaper is presented as a combination of text, image, and graphics. This has a different impact on the user than the information presented on the television as a combination of image, photo, video, sound and music. Similarly, talking over a telephone (using sound) has a different impact on the user, than, talking using the Internet telephone with a web camera (sound and photo) attached to it. In other words, the same information when presented using different media has a different impact on the user. Or, we can say that the media used for presenting the information affects the way the user perceives and understands the information. Multimedia is a combination of graphics, audio, text, animation, and video using the computer.
Multimedia: Definition
Newspaper, radio, television and films are some of the earliest and traditional means of mass communication that use mass media. Newspapers use text, image and graphics, and, television uses text, image, graphics, and sound (Figure 13.1). In these traditional means of communication, the communication is one-way—from the media to the mass users. The user simply reads the newspaper, listens to the radio, and watches the television and films, and, cannot in any way manipulate the media. Mass media is used by the user in a sequence, linearly. For example, a text book consists of a sequence of combination of text, graphics, and images. The text book is meant to be read linearly from the start to the end. With mass media, the user is in a passive state (receiving whatever is communicated).
Figure 13.1. Mass media


Elements of Multimedia
A multimedia system consists of several elements like—text, graphics, sound, video, andanimation. The data streams of these different elements of the multimedia system are of two kinds—time-dependent, and time-independent. Media like text, graphics, and image are time-independent. The information is not dependent on the timing of the data stream when using these media. However, media like audio, video, and animation are time-dependent. In time-dependent media, the data streams must appear at regular time intervals for the purposes of continuity.
Multimedia System
The multimedia system includes the hardware and software components that are required to be used for multimedia. The hardware and software components required for a multimedia system are as follows:
• Input Devices— Keyboard and OCR for text; Digital cameras, Scanners and CD-ROM for graphics, MIDI keyboards, CD-ROM and microphones for sound; Video cameras, CD-ROM and frame grabbers for video; Mice, trackballs, joy sticks, virtual reality gloves and wands for spatial data; and mouse, touch screen, trackball, tablet, voice recognition system, infrared remotes, magnetic card encoder and reader, 3D input devices, and virtual reality devices.
• Output Devices— CD-quality speakers, Hi-resolution monitors, color printers, specialised helmets, and immersive devices displays for virtual reality, and video devices.
• Storage Devices— Hard disks, CD-ROM drive, Zip drive, DVD drive.
• Communication Network— Ethernet, Token Ring, FDDI, ATM, Intranets, and Internets.
• Communication Devices— Modem, Network Interface Card.
• Computer System— Multimedia Desktop machine, Workstation, MPEG/VIDEO hardware
• Software— Some of the familiar tools for multimedia software are—Word Processor (MS-WORD, WordPerfect), Spreadsheet (MS-Excel), Database (Q+E Database/VB), and, Presentation Tools (MS-PowerPoint). Some of the software tools used for different elements of multimedia are as follows—
o Digital Audio—Cool Edit, Sound Forge, Pro Tools, Audacity
o Image Editing—Adobe Photoshop, Macromedia Fireworks
o Video Editing—Adobe Premiere, Windows Movie Maker, iMovie
o Animation—3D Studio Max, Maya

Multimedia Applications
Multimedia applications have found their way into different arenas of our life. We are interacting with multimedia applications in the area of education and entertainment that includes sports, laser shows, video games, or animation movies. Multimedia applications have found their way in business—may it be for advertising, marketing, video meetings, result presentations or customer feedbacks. Nowadays, training is also imparted using multimedia applications like simulations and 3D designs. Entertainment parks like Disneyland use virtual reality and multimedia, innovatively design, create, and improve; their games and rides. The following subsections discuss the impact of multimedia applications in different areas of our life.

13.6.1. In Education
Using multimedia for education encompasses the use of video clips, speech and sound, music, animations, and graphics. The use of these multimedia elements impacts the whole learning process and pedagogy. It is always better to visually observe and hear about a topic than only reading it from a book.

Computer Security
Introduction
We all like to be secure in our home, office, locality, city, country, and in this world. We use different mechanisms to ensure our security. Inside our homes, we keep our valuables safely locked in a cupboard that is accessible by the elders of the house; we keep the gates of our house bolted and even have an intrusion-detection system installed. We have high walls and gates surrounding our locality and also a watchman who guards the open gates. We have police for our security within a city and armed forces for the country. We take all these measures to make ourselves and our valuables, resources, possessions secure.
The widespread use of computers has resulted in the emergence of a new area for security—security of computer. Computer security is needed to protect the computing system and to protect the data that they store and access. Transmission of data using network (Internet) and communication links has necessitated the need to protect the data during transmission over the network. Here, we use the term computer security to refer to both the computer security and the network security.
Security Threat and Security Attack
A threat is a potential violation of security and causes harm. A threat can be a malicious program, a natural disaster or a thief. Vulnerability is a weakness of system that is left unprotected. Systems that are vulnerable are exposed to threats. Threat is a possible danger that might exploit vulnerability; the actions that cause it to occur are the security attacks. For example, if we leave the house lock open—it is vulnerable to theft; an intruder in our locality (might exploit the open lock)—is a security threat; the intruder comes to know of the open lock and gets inside the house—This is a security attack.
A security attack may be a passive attack or an active attack.
Malicious Software
Malicious users use different methods to break into the systems. The software that is intentionally included into a system with the intention to harm the system is calledmalicious software. Viruses, Trojan horse, and Worms are examples of malicious programs. Java scripts and Java applets written with the purpose of attacking, are also malicious programs.
14.3.1. Virus
Virus is a software program that is destructive in nature. Virus programs have the following properties:


Hacking
Hacking is the act of intruding into someone else’s computer or network. A hacker is someone who does hacking. Hacking may result in a Denial of Service (DoS) attack. The DoS attack prevents authorized users from accessing the resources of the computer. It aims at making the computer resource unusable or unavailable to its intended users. It targets the computer and its network connections, to prevent the user from accessing email, web sites, online accounts (banking, etc.), or other services that rely on the affected computer. In a DoS attack, the services of the entire network, an Internet site or service, may be suppressed or disabled. The affected machine is flooded with spurious requests and messages so as to overload the network. As a result, the affected machine cannot process the valid requests. This is a denial of service to the valid users. Generally, the targets of such attacks are the sites hosted on high-profile web servers such as banks and credit card payment gateways.
Packet sniffing, E-mail hacking and Password cracking are used to get the username and password of the system to gain unauthorized access to the system. These methods gather the information when the data is being transmitted over the network.
Security Mechanisms
Security mechanisms deal with prevention, detection, and recovery from a security attack. Prevention involves mechanisms to prevent the computer from being damaged. Detection requires mechanisms that allow detection of when, how, and by whom an attacked occurred. Recovery involves mechanism to stop the attack, assess the damage done, and then repair the damage.
Security mechanisms are built using personnel and technology.

Digital Signature
A signature on a legal, financial or any other document authenticates the document. A photocopy of that document does not count. For computerized documents, the conditions that a signed document must hold are—(1) The receiver is able to verify the sender (as claimed), (2) The sender cannot later repudiate the contents of the message, (3) The receiver cannot concoct the message himself. A digital signature is used to sign a computerized document. The properties of a digital signature are same as that of ordinarysignature on a paper. Digital signatures are easy for a user to produce, but difficult for anyone else to forge. Digital signatures can be permanently tied to the content of the message being signed and then cannot be moved from one document to another, as such an attempt will be detectable.
Digital signature scheme is a type of asymmetric cryptography. Digital signatures use the public-key cryptography, which employs two keys—private key and public key.

Other Security Measures
In addition to the above discussed security techniques, several other security techniques are used for security purposes. Some of these are listed below:
• Intrusion Detection Systems— They complement firewalls to detect if internal assets are being hacked or exploited. A Network-based Intrusion Detection monitors real-time network traffic for malicious activity and sends alarms for network traffic that meets certain attack patterns or signatures. A Host-based Intrusion Detection monitors computer or server files for anomalies and sends alarms for network traffic that meets a predetermined attack signature.
• Virus Protection Software— They should be installed on all network servers, as well as computers. They screen all software coming into your computer or network system (files, attachments, programs, etc.) preventing a virus from entering into the system.
• Data and Information Backups— It is required for disaster recovery and business continuity. Back-ups should be taken daily and periodically (weekly) and should be kept for at least 30 days while rotating stockpile.

Computer Practicals
Windows XP
Contents
• Introduction
• Features of Windows XP
• The desktop—The task bar, the icons and shortcuts
• Structure of Windows—Title bar, menu bar, tool bar, scroll bar, status bar
• Windows XP explorer
o The start
o The window—Title bar, menu bar, standard bar, address bar, status bar
o The view—Filmstrip, thumbnails, tiles, icons, list, details
o Selecting files
o Working with folders—Creating, deleting, copying, moving, changing
o Files and folders properties—Showing, organizing, modifying
o The search
o The recycle bin—Open, restoring and deleting files or folders, emptying
o Configuring screen—Desktop, screen saver, appearance, themes, settings
o Configuring the mouse, adding or removing programs
o Adding new hardware—Not plug & play, basic information about computer
o System tools—Backup, character map, disk cleanup, system restore etc.
o The scandisk
o Windows XP media player, Windows XP help
o Windows vista—Updated GUI, Windows instant search, Windows DVD maker, embedded start menu, the taskbar preview, Windows contacts
o Windows 7—Desktop, Windows explorer, taskbar, devices, virtual hard disk, Windows action center, Windows biometric framework, wordpad

Introduction
There exist a number of operating systems, such as DOS, Windows 98, Windows NT, Windows XP, Windows Vista, Unix, Linux, DOS, Mac OS X Snow Leopard etc. Each Operating System (OS) has its own unique features. Windows XP belongs to the Windows family of OS. Windows XP represents an important change from the previous versions of Windows OS. Before Windows XP, Microsoft had two different operating systems, Windows 98 for personal use and Windows NT/2000 for business and professional environment. Windows XP is a convergence among both versions; the center of operating system Windows 2000 was divided to create Windows XP, and some adjustments were done to differentiate Windows XP Home Edition and Windows XP Professional.
Features of Windows XP
Windows XP has a new user system completely different from Windows 98. Some new features of Windows XP are:
• Multiple users with independent profiles can be defined. Each user can have different permissions that will allow the user to carry out certain tasks. Each user will have a different Start menu and My Documents folder that can be protected by password. Multiple users can also share folders. The system handles the different active users without interferences.
• It is better integrated to Internet Explorer.
• CDs can be burned by dragging and dropping to the recording unit. It is no longer necessary to install an additional program to record CDs.
• It has a useful way for showing pictures called Filmstrip.
• It’s easier to configure a domestic network.
• It recovers better from errors. When a fatal error occurs Windows XP creates a register with all the information concerning the error and gives user the option of sending it to Microsoft, to be analyzed.
• Windows XP initializes faster than Windows 98.
• The Start menu and the Task bar have changed.
• Windows Movie Maker is a new component used for editing films.

The Desktop
The entire screen on which all windows are displayed is termed as Windows Desktop. It is the first screen that appears when the operating system has initialized (Figure 15.1). All your work opens as individual windows on the Windows Desktop.
Figure 15.1. The desktop screen
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Windows XP Explorer
Windows Explorer lets the user explore the contents of computer and do file management. It organizes and controls the files and folders of the different storage devices such as the hard drive, disk drive, etc. The Windows Explorer is also known as the File Manager. Windows Explorer is especially useful for copying and moving files. Windows Explorer allows to delete, see, copy, or move files and folders.
The Search
With so many files and folders, sometimes it becomes difficult to locate a file or a folder in the directory. Windows XP provides Search option to search for hardware, a network, people in the directory, Internet pages, etc. To search click <Start><Search>.
It allows you to search for files and folders, people, hardware, and on the Internet. The search pop-up screen will be displayed
The Recycle Bin
The Recycle Bin is a space on the hard disk reserved to store information that is deleted. In the event of deleting a file or folder by mistake, it is possible to retrieve it from the Recycle Bin. If a deleted file needs to be restored, the Recycle Bin restores files or folders to the place from where they were deleted. For example, if a file is deleted from D:\My Documents, when it is restored, it will go back to this folder. Recycle Bin stores and maintains the deleted documents until the bin is emptied.
• Open Recycle Bin— To open the Recycle Bin, place the cursor on Desktop and double-click on the Recycle Bin icon  . The Recycle Bin window (Figure 15.16) is similar to the Windows Explorer window, and has similar options. In the Recycle Bin shows the names of the deleted files and folders, their original location before it was deleted and the date and time when it was deleted.
Figure 15.16. The recycle bin
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• Restoring Files or Folders
o Select the elements to be restored by clicking on them.
o Click on the green arrow on the left side with <Restore the selected Items> or <Restore this Item> depending on whether you have selected more than one item or one item, or, Click on <File><Restore>
o The selected files will return to where they were located before deletion.
• Deleting Files or Folders— Once files and folders in the Recycle Bin are deleted, they are deleted permanently. To delete any file or folder from the Recycle Bin follow these steps:
o Select the files to be deleted.
o <File><Delete>, or, press the Delete button on the keyboard.
o A window appears asking if you are sure that you want to delete the selected file or folder. Click Yes if you are sure you want it deleted.
o The selected files will disappear and cannot be restored.
• Emptying the Recycle Bin— There are three ways to empty the Recycle Bin as follows—
o Open Recycle Bin Window. Click on <Empty the Recycle Bin>. A window will appear asking “Are you sure you want to delete these x items”, where x is the number of elements currently in the Recycle Bin. Click Yes to empty it.
o Open Recycle Bin window. <File><Empty Recycle Bin>. A window will appear asking “Are you sure you want to delete these x items”, where x is the number of elements currently in the Recycle Bin. Click Yes to empty it.
o Right click on the Recycle Bin icon   on the desktop. <Empty Recycle Bin>

Configuring the Screen
A user spends long hours in front of the computer. Configuration of the screen is required to make the screen of the desktop comfortable for use. The user can configure the desktop screen as follows:
1. On the Desktop, Right click on the screen where there are no icons on the screen.
2. Select <Properties>. It will display the properties of the screen. It contains tabs like the Desktop, Screen saver, Appearance, Themes, and Settings.

Control Panel
Adding or Removing Programs
The Adding and Removing tool is used to add a program and to uninstall a program that is no longer needed. When a new program is installed, Windows creates notes on a file called Windows Register. The Windows Register stores the current configuration of the system, hardware, software, and different user configurations. A program that needs to be uninstalled cannot be done by simply deleting the files manually. If we delete, only the files linked to a program, the records that Windows created on the Register are not removed, so an inconsistency can occur.
Adding New Hardware
When we want to add new hardware to a computer, two things can happen: either the component is Plug & Play or it is not. If the hardware to be installed is Plug & Play, simply connect the hardware and Windows will recognize and install it automatically. Conversely, if you connect the hardware and the Window recognizes it, then the hardware is Plug & Play. If the Windows does not recognize it, then the element is not Plug & Play and needs to be installed manually. For installing it, an Add new Hardware assistant is provided. When new hardware is installed, the computer needs driver for that hardware. The driver contains the files that describe the hardware and allows the computer to communicate with it.
• To add a hardware that is not plug & play, open the window as follows—
o <Start><Settings><Control Panel><Printers and Other Hardware><Add hardware> (on the left of window) (Figure 15.22)
Figure 15.22. The window and other hardware screen
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o The Add Window Hardware Wizard appears. Follow the instructions of the wizard for installation.
• To see the basic information about your computer like the hardware of your system and their properties, do the following:
o <Start><Control Panel><Performance and maintenance><See basic information about your computer>
o A window named System Properties will appear. It has various tabs. For example, the General tab shows generic information about your system, such as which processor is installed, etc. Select <Hardware><Device manager>. It shows a list of all the hardware installed on your computer
System Tools
Windows incorporates certain tools such as the Disk Defragmenter, the Disk Cleanup - the tool to free disk space, the Scheduled Tasks, etc. Almost all of these tools are designed to optimize the behavior of the computer.
The Scandisk
It is a tool used to search errors in the system’s units and to repair those errors. When the computer is turned off in an abrupt manner it is possible that some files may get damaged. Normally when the computer is turned on, after being turned off abruptly (without using the option shut down from the Start menu), the Scandisk executes to check the system and repair any error that it may find. By using this tool we can fix the possible errors and therefore retrieve the information that it contains, although, it is not always possible to retrieve the information.
Windows XP Media Player
Windows XP includes the Windows Media Player (Figure 15.28) which allows you to listen to music from a CD. To open the Windows Media Player double click on  . It allows playing of songs from a CD or from the hard disk drive. There are commands to handle the player, like play as well as to pause, stop the song or video being played, skip back to the previous song on the list, skip to the next song or video on the playlist, move forward or move backward in a song, control the volume and you can do many more things.
Figure 15.28. The windows media player
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Windows XP Help
The Windows XP provides help to questions regarding the use of a Windows XP component or tool. The help is composed of a series of pages that are similar in navigation, as the pages on a web site. Options are also available to search information about a particular theme from key words and key phrases.
Windows Vista
Windows Vista contains many changes and new features over its predecessor (Windows XP).
Microsoft’s Windows Vista operating system is designed to give better results in less time. Its improved graphics look helps in multitasking, and its increased security system makes your data more secure but it needs very high systems specifications to run. The minimum specification of the computer on which Windows Vista can be installed is Pentium 4 or higher, 512 MB RAM, 32 MB video card and 40 GB hard disk. But, Windows Vista installed on the computer having the above specification makes the computer very slow. To have a reasonable speed of working with Windows Vista installed, you should have at least 2.0 GHz Pentium 4 or higher, 1 GB of RAM, 60 GB hard disk and 64 MB video RAM. The high system requirements are one of the key reasons for Windows Vista criticism.


Windows 7
Windows 7 makes the most of powerful 64-bit PCs, the new desktop standard. It includes several feature advancements in touch, speech, handwriting recognition, support for virtual hard disk, and support for additional file formats, improved performance on multicore processors, improved boot performance, and kernel improvements. It includes performance improvements like sleep and resume quickly, and spot USB devices faster. It retains Windows Aero user interface and visual style introduced with Windows Vista.
Questions
1. What is the benefit of Windows XP over its predecessors?
2. List any five new features of Windows XP.
3. What is Windows Desktop?
4. Discuss about the different parts of Windows desktop screen.
5. Name the different parts of the Task Bar.
6. In which area does the date and time appear on the Windows screen.
7. List the different ways in which you can organize icons on desktop (Arrange icons by).
8. Describe the structure of Window in Windows XP.
9. Write steps to do the following —(1) Organizing icons on Desktop, (2) Create Shortcuts, and (3) Change Date and Time.
10. What is the purpose of the title bar, menu bar, tool bar, scroll bar and status bar in a Window of Windows XP.
11. What is the purpose of Windows XP Explorer?
12. List the different views in which you can see the folder information.
13. Explain in one or two lines, how the folder information is viewed in (1) Filmstrip, (2) Thumbnails, (3) Tiles, (4) Icons, (5) List, and (6) Details.
14. List the different ways of selecting a file or a folder.
15. Write steps to do the following—(1) Create a Folder, (2) Delete a File, (3) Copy a File, (4) Move a File, and (5) Change the name of a File.
16. What information is provided by the <Properties> of the folder.
17. Write steps to do the following—(1) Show Hidden Files and Folders, (2) Know the Types of Files, and (3) Organize Folders.
18. What is the purpose of Recycle Bin?
19. List the steps to restore a file from Recycle Bin.
20. List the steps to configure Desktop, Screen saver, and Screen appearance.
21. What is the purpose of Windows Register?
22. List the steps to add a non-plug & play hardware.
23. Name any three System tools.