INTRODUCTION TO INFORMATION
TECHNOLOGY
UNIT -2
COMPUTER SOFTWARE
• Computer software (often called just software) is a set of
instructions and associated documentation that tells a computer what to do or how to perform a task or it can mean all the software on a computer, including the applications and the operating system.
APPLICATION SOFTWARE
• A normal user rarely gets to see the operating system or to work with it.
But all of us are familiar with application software which we must use to interact with a computer. Popular examples of application software are the Microsoft office suite which includes Word, Excel and PowerPoint. We use these applications extensively.
• Internet explorer, Mozilla Firefox, Chrome are applications used to access the internet. E-mail software like Outlook express is used to manage Emails. It is obvious that all software utilized for working on a computer is classified as application software. In fact all user interfaces are an application. The anti-virus is an application and so is the Media player
SYSTEM SOFTWARE
• System software is a type of computer program that is designed to run a computer’s hardware and application programs. If we think of the computer system as a layered model, the system software is the interface between the hardware and user applications.
• The operating system (OS) is the best-known example of system software.
The OS manages all the other programs in a computer. The OS coordinates the different hardware components of a computer.
• Other examples of system software and what each does:
• The BIOS (basic input/output system) gets the computer system started after you turn it on and manages the data flow between the operating system and attached devices such as the hard disk, video adapter, keyboard, mouse, and printer.
SYSTEM SOFTWARE
• The boot program loads the operating system into the computer's main memory or random access memory (RAM).
• An assembler takes basic computer instructions and converts them into a pattern of bits that the computer's processor can use to perform its basic operations.
• A device driver controls a particular type of device that is attached to your computer, such as a keyboard or a mouse. The driver program converts the more general input/output instructions of the operating system to messages that the device type can understand
SYSTEM SOFTWARE
• System software is responsible for managing a variety of independent hardware components, so that they can work together in harmony.
• Its purpose is to unburden the application software programmer from the often complex details of the particular computer being used, including such accessories as communications devices, printers, device readers, displays and keyboards, and also to partition the computer's resources such as memory and processor time in a safe and stable manner.
ASSEMBLER
• A computer will not understand any program written in a language, other than its machine language. The programs written in other languages must be translated into the machine language. Such translation is performed with the help of software.
• A program which translates an assembly language program into a machine language program is called an assembler.
• If an assembler which runs on a computer and produces the machine codes for the same computer then it is called self assembler or resident assembler. If an assembler that runs on a computer and produces the machine codes for other computer then it is called Cross Assembler.
ASSEMBLER
• Assemblers are further divided into two types:
• 1. One Pass Assembler
• 2. Two Pass Assembler.
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• One pass assembler is the assembler which assigns the memory addresses to the variables and translates the source code into machine code in the first pass simultaneously.
• A Two Pass Assembler is the assembler which reads the source code twice. In the first pass, it reads all the variables and assigns them memory addresses. In the second pass, it reads the source code and translates the code into object code.
COMPILER
• It is a program which translates a high level language program into a machine language program.
• A compiler is more intelligent than an assembler. It checks all kinds of limits, ranges, errors etc. But its program run time is more and occupies a larger part of the memory.
• It has slow speed. Because a compiler goes through the entire program and then translates the entire program into machine codes.
• If a compiler runs on a computer and produces the machine codes for the same computer then it is known as a self compiler or resident compiler. On the other hand, if a compiler runs on a computer and produces the machine codes for other computer then it is known as a cross compiler.
INTERPRETER
• An interpreter is a program which translates statements of a program into machine code. It translates only one statement of the program at a time.
• It reads only one statement of program, translates it and executes it.
Then it reads the next statement of the program again translates it and executes it. In this way it proceeds further till all the statements are translated and executed.
• On the other hand, a compiler goes through the entire program and then translates the entire program into machine codes. A compiler is 5 to 25 times faster than an interpreter.
INTERPRETER
• By the compiler, the machine codes are saved permanently for future reference. On the other hand, the machine codes produced by interpreter are not saved.
• An interpreter is a small program as compared to compiler. It occupies less memory space, so it can be used in a smaller system which has limited memory space.
DIFFERENCE
COMPILER INTERPRETER
• Translates program one statement at a time.
• It takes less amount of time to analyze the source code but the overall execution time is slower.
• Continues translating the program until the first error is met, in which case it stops. Hence debugging is easy.
• Programming language like Python, Ruby use interpreters.
• Scans the entire program and translates it as a whole into machine code.
• It takes large amount of time to analyze the source code but the overall execution time is comparatively faster.
• It generates the error message only after scanning the whole program.
Hence debugging is comparatively hard.
• Programming language like C, C++
use compilers.
LINKER
• In high level languages, some built in header files or libraries are stored.
These libraries are predefined and these contain basic functions which are essential for executing the program. These functions are linked to the libraries by a program called Linker.
• If linker does not find a library of a function then it informs to compiler and then compiler generates an error. The compiler automatically invokes the linker as the last step in compiling a program.
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LINKER
• Not built in libraries, it also links the user defined functions to the user defined libraries.
• Usually a longer program is divided into smaller subprograms called modules. And these modules must be combined to execute the program. The process of combining the modules is done by the linker.
LOADER
• Loader is a program that loads machine codes of a program into the system memory.
• In Computing, a loader is the part of an Operating System that is responsible for loading programs. It is one of the essential stages in the process of starting a program. Because it places programs into memory and prepares them for execution.
• Loading a program involves reading the contents of executable file into memory. Once loading is complete, the operating system starts the program by passing control to the loaded program code.
• All operating systems that support program loading have loaders. In many operating systems the loader is permanently resident in memory.
OPERATING SYSTEM
• An operating system is a program that manages the computer hardware.
• It also provides a basis for application programs and acts as an intermediary between the user and the computer hardware.
• The purpose of an operating system is to provide an environment in which a user can execute programs in a convenient and efficient manner.
• A computer system can be divided roughly into four components:
The hardware – the CPU, the memory, and the I/O devices provides the basic computing resources for the system.
The application programs – such
as word processors,
spreadsheets define the ways in which these resources are used to solve users’ computing problems.
The operating system controls and coordinates the use of the hardware among various application programs for the various users.
OPERATING SYSTEM SERVICES
• An Operating system provides an environment for the execution of programs. Operating system services are provided for the convenience of
the programmer, to make the programming task easier.
• User Interface – CLI, GUI
• Program Execution – Load, Run, terminate (Normally, Abnormally)
• I/O Operations – To ensure efficiency and protection, users cannot control I/O devices directly.
• File –system manipulation – permission management, file ownership
• Communications – Shared memory, message passing
• Error Detection – OS should ensure correct and consistent computing
• Resource Allocation – CPU cycles, main memory, files, I/O devices
• Accounting – Usage statistics – helps to reconfigure the system
• Protection and security – Access to system resources should be controlled.
TYPES OF
OPERATING SYSTEM
BATCH OPERATING SYSTEM
• The users of a batch operating system do not interact with the computer directly. Each user prepares his job on an off-line device like punch cards and submits it to the computer operator. To speed up processing, jobs with similar needs are batched together and run as a group. The programmers leave their programs with the operator and the operator then sorts the programs with similar requirements into batches.
• The problems with Batch Systems are as follows −
• Lack of interaction between the user and the job.
• CPU is often idle, because the speed of the mechanical I/O devices is slower than the CPU.
• No mechanism to prioritize the processes. Difficult to provide the desired priority.
TIME SHARING OPERATING SYSTEM
• Time-sharing or multitasking is a logical extension of multiprogramming.
• The main difference between Multiprogrammed Batch Systems and Time-Sharing Systems is that in case of Multiprogrammed batch systems, the objective is to maximize processor use, whereas in Time-Sharing Systems, the objective is to minimize response time.
TIME SHARING OPERATING SYSTEM
• Multiple jobs are executed by the CPU by switching between them, but the switches occur so frequently. Thus, the user can receive an immediate response.
• For example, in a transaction processing, the processor executes each user program in a short burst or quantum of computation. That is, if n users are present, then each user can get a time quantum.
When the user submits the command, the response time is in few seconds at most.
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TIME SHARING OPERATING SYSTEM
• The operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time.
• Advantages of Timesharing operating systems are as follows −
• Provides the advantage of quick response.
• Reduces CPU idle time.
• Avoids duplication of software.
TIME SHARING OPERATING SYSTEM
• Much more expensive to develop
• Hard to implement
• The big disadvantages of time sharing systems is that it consumes much resources so it need special operating systems.
• Switching between tasks becomes sometimes unsophisticated as there are lot of users and applications running which may hang up the system. So the time sharing systems should have high specifications of hardware.
DISTRIBUTED OPERATING SYSTEM
• Data processing jobs are distributed among the processors accordingly.
• The processors communicate with one another through various communication lines (such as high-speed buses or telephone lines).
These are referred as loosely coupled systems or distributed systems.
Processors in a distributed system may vary in size and function.
These processors are referred as sites, nodes, computers, and so on.
DISTRIBUTED OPERATING SYSTEM
The advantages of distributed systems are as follows −
• With resource sharing facility, a user at one site may be able to use the resources available at another.
• Speedup the exchange of data with one another via electronic mail.
• If one site fails in a distributed system, the remaining sites can potentially continue operating.
• Better service to the customers.
• Reduction of the load on the host computer.
• Reduction of delays in data processing.
DISTRIBUTED OPERATING SYSTEM - TYPES
• Client/Server Systems
• The client-server architecture is a way to dispense a service from a central source.
• There is a single server that provides a service, and multiple clients that communicate with the server to consume its products.
• In this architecture, clients and servers have different jobs. The server's job is to respond to service requests from clients, while a client's job is to use the data provided in response in order to perform some task
DISTRIBUTED OPERATING SYSTEM - TYPES
• The term peer-to-peer is used to describe distributed systems in which task is divided among all the components of the system. All the computers send and receive data, and they all contribute some processing power and memory. As a distributed system increases in size, its capacity of computational resources increases. In a peer-to-peer system, all components of the system contribute some processing power and memory to a distributed computation.
NETWORK OPERATING SYSTEM
• A Network Operating System runs on a server and provides the server the capability to manage data, users, groups, security, applications, and other networking functions. The primary purpose of the network operating system is to allow shared file and printer access among multiple computers in a network, typically a local area network (LAN), a private network or to other networks.
• Examples of network operating systems include Microsoft Windows Server 2003, Microsoft Windows Server 2008, UNIX, Linux
NETWORK OPERATING SYSTEM
The advantages of network operating systems are as follows −
• Centralized servers are highly stable.
• Security is server managed.
• Upgrades to new technologies and hardware can be easily integrated into the system.
• Remote access to servers is possible from different locations and types of systems.
The disadvantages of network operating systems are as follows −
• High cost of buying and running a server.
• Dependency on a central location for most operations.
• Regular maintenance and updates are required.
REAL TIME OPERATING SYSTEM
• A real-time system is defined as a data processing system in which the time interval required to process and respond to inputs is so small that it controls the environment.
• The time taken by the system to respond to an input and display of required updated information is termed as the response time. So in this method, the response time is very less as compared to online processing.
• Real-time systems are used when there are rigid time requirements on the operation of a processor.
REAL TIME OPERATING SYSTEM
• A real-time operating system must have well-defined, fixed time constraints, otherwise the system will fail. For example, Scientific experiments, robots, air traffic control systems, etc.
• There are two types of real-time operating systems.
• Hard real-time systems
• Hard real-time systems guarantee that critical tasks complete on time.
In hard real-time systems, secondary storage is limited or missing and the data is stored in ROM. In these systems, virtual memory is almost never found.
REAL TIME OPERATING SYSTEM
• Soft real-time systems
• Soft real-time systems are less restrictive.
• A critical real-time task gets priority over other tasks and retains the priority until it completes.
• Soft real-time systems have limited utility than hard real-time systems.
• For example, multimedia, Advanced Scientific Projects like undersea exploration ETC.
APPLICATION
SOFTWARE
APPLICATION SOFTWARE
• While system software comprises device drivers, OS, servers and software components, programming software helps in writing programs through tools such as editors, linkers, debuggers, compilers/interpreters and ore. Application software , in contrast to these two, is used for attaining specific tasks.
• Application software uses the capacity of a computer directly for specific tasks and are used to manipulate text, graphics and numbers.
APPLICATION SOFTWARE
• An application program (app or application for short) is a computer program designed to perform a group of coordinated functions, tasks, or activities for the benefit of the user. Examples of an application include a word processor, a spreadsheet, an accounting application, a web browser, a media player, a console game or a photo editor.
APPLICATION SOFTWARE
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Features of application software are as follows −
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Close to the user
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Easy to design
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More interactive
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Slow in speed
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Generally written in high-level language
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Easy to understand
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Easy to manipulate and use
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