Planning a Computer Program

PLANNING A COMPUTER PROGRAM

Planning a computer program means planning the logic of a program.  In order to produce a correct and effective computer program, the logic of the program must be planned first.  Without the logic, we can’t write the program well.

While writing a computer program, all the instructions must be written in a proper sequence.  When the order is not correct or some of the instructions are left out, the computer will calculate a wrong answer.  To ensure the correct order and the appropriateness of the computer instructions, a program must be planned first.  Planning a computer program is done with the help of planning tools and techniques, which include Algorithm, Flowchart and Pseudo code.

A sequence of instructions is called an algorithm.  Writing good algorithms is a fundamental part of programming.  There are two commonly used tools available for documenting the program logic (algorithm).  They are: flowcharts and Pseudocode. Generally, flowcharts work well for small problems but Pseudocode is used for larger problems.

Have a presentation on problem solving using Computers here:
 

Writing Algorithm:

The term algorithm refers to the logic of the program.  An algorithm is defined as a step-by-step description of how to arrive at the solution of a given problem.  An algorithm contains a set of instructions that must be executed in a specified sequence to produce the desired result.

The characteristics of a good algorithm are listed below:

1. Each and every instruction should be precise and unambiguous.
2. Each instruction should be designed in such a way that it can be performed in a finite time.
3. Not a single instruction should be repeated infinitely, i.e., there should be an end for an algorithm both logically and physically.
4. After the termination of an execution, the user must be able to get the desired output.

The following are three different ways in which an algorithm can be represented:

1. As Programs
2. As Flowcharts
3. As Pseudo codes

The first one is the language representation of an algorithm.  A program can be compiled and executed by a computer to produce an expected output. When a high-level language is used for representing an algorithm, it becomes a computer program.  The syntax and semantics of the particular programming language must be followed to write the program in it.

Normally algorithms are written in simple and plain English.  No rules and regulations are formed for writing algorithms except some characteristics, which qualify a set of instructions to be an algorithm.  To represent algorithms pictorially flowcharts are used.

Designing Flowcharts:

A flowchart is a pictorial representation of an algorithm.  Programmers often use it as a visual tool for organizing the sequence of steps necessary to solve a problem.  It can be considered as pictorial representation of a program.  The process of drawing a flowchart for an algorithm is often referred to as flowcharting.  Flowcharting is a task that must be done after writing the algorithm for a computer program. 

A set of symbols is provided for drawing flowcharts that represent different operations to be done by a computer.  The symbols used in a flowchart are connected together using arrow headed solid lines to indicate the sequence in which the instructions must be evaluated. Some of the common symbols used in flowcharts are shown below:

With flowcharting, essential steps of an algorithm are shown using the shapes above. The flow of data between steps is indicated by arrows, or flowlines.

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A Book on Fundamentals of Computing & Computer Programming

This book is all about Fundamentals of Computers and Computer Programming.  It would be a useful resource for the students who are doing their first year of Engineer degree in any discipline, which includes CSE, IT, ECE, EEE, MECH and CIVIL branches.

To get a copy of this book follow the link given below:

Please mail me if you are interested in having a copy of this book, to davidjlivingston@gmail.com

To get a copy of this book in person we charge Rs. 200/-

To get it through post in India, we charge Rs. 250/-

A part of the books is available for Students' use.  Download it here!

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A Course on Fundamentals of Computing for Engineers

FUNDAMENTALS OF COMPUTING AND COMPUTER PROGRAMMING

AIM :

• To provide an awareness to Computing and Programming

OBJECTIVES :

• To enable the student to learn the major components of a computer system

• To know the correct and efficient ways of solving problems

• To learn to use office automation tools

• To learn to program in C

UNIT I - INTRODUCTION TO COMPUTERS

Introduction – Characteristics of Computers – Evolution of Computers - Computer

Generations – Classification of Computers – Basic Computer organization – 

Number Systems

UNIT II - COMPUTER SOFTWARE

Computer Software –Types of Software – Software Development Steps – Internet

Evolution - Basic Internet Terminology – Getting connected to Internet 

Applications.

UNIT III - PROBLEM SOLVING AND OFFICE AUTOMATION

Planning the Computer Program – Purpose – Algorithm – Flow Charts –

Pseudocode - Application Software Packages- Introduction to Office Packages

(not detailed commands for examination).

UNIT IV - INTRODUCTION TO C

Overview of C – Constants, Variables and Data Types – Operators and

Expressions – Managing Input and Output operators – Decision Making - 

Branching and Looping.

UNIT V - FUNCTIONS AND POINTERS

Handling of Character Strings – User-defined Functions – Definitions –

Declarations - Call by reference – Call by value – Structures and Unions – Pointers

– Arrays – The Preprocessor – Developing a C Program : Some Guidelines

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Need for Software in Computers

HARDWARE & SOFTWARE 

The physical devices used to form a computer are called Computer Hardware. Examples for computer hardware are: Monitor, Keyboard, Printer, Hard Disk Drive, and Floppy Disk Drive etc. Computer hardware is responsible for implementing all necessary operations such as accepting user input, storing data, performing calculations, and displaying or printing results.

Hardware can’t operate on its own. To make them work, we need a set of programs called Software. Software that runs on PCs can be classified into four major categories:

1. Operating Systems like DOS, Windows 95 and UNIX
2. Programming languages such as Basic, Fortran, COBOL, and C++
3. Application programs/packages such as Word Processors, Spreadsheet, and Database Management Systems
4. Other application programs that can do a specific job such as Accounting, Payroll, Billing, Weather forecasting and Ticket Reservation software

Software

Software consists of computer programs that control the operations of computer hardware. Computer programs are nothing but sequence of instructions given by a programmer to perform certain operations on the computer. One of the most critical functions of software is to direct the workings of computer hardware. There are two basic types of software: System software and Application software.

System Software

System software is a set of programs designed to coordinate the activities and functions of hardware as well as various programs running on the hardware. System software is more system dependant and is designed for a particular hardware configuration. The combination of both hardware and the system software used for accessing the hardware is known as computer system Platform.

The main use of system software is to control the operations of computer hardware and to support the application programs problem-solving capabilities. An Operating System is one of the system software, which acts as an interface or layer between the user and the computer hardware. It also acts as a Resource Allocator, which manages and allocates resources to specific programs and users for performing various tasks on the computer.

Operating System

An OS consists of control routines for operating a computer and provides an environment for the execution of programs. It may be viewed as an organized collection of Software extension to hardware. The following are the two major goals of an OS:

1. To provide users convenience in operating the system.
2. To make use of the computer hardware efficiently.

The services provided by an OS can be accessed either directly or indirectly through an application program. Users may interact with the OS directly by means of its commands. Application programs have to user the Operating System API calls to access the computer resources like files and I/O devices.

The primary objective of an OS is to increase the productivity of computer hardware. OS may process its workload serially or concurrently. That is, resources in a computer system may be dedicated to a single program until its completion, or they may be allocated dynamically (whenever required) to execute multiple programs simultaneously.

Potential benefits of concurrent execution of multiple programs include increased performance, resource utilization and responsiveness of a computer system. In a multiprogramming OS, multiple active programs share the system resources like processor, memory and I/O devices.

Have an introduction to Operating System in a presentation here:

Operating System Functionalities

An OS is a set of computer programs that controls the computer hardware and acts as an interface between the application software and the hardware. Every OS is usually stored on disk (primary or secondary) and in files. For instance, DOS bundles its functions in a set of files, such as Command.com, Edit.exe, and Copy.exe.

In Windows, the major functionalities are provided in three Dynamic Link Library (DLL) files: GDI32.DLL, KERNAL32.DLL and USER32.DLL. As soon as a computer system is started, portions of the OS are transferred to memory as they are needed. The various functionalities provided by an OS are listed below:

1. Performing common computer hardware functions
2. Providing a User Interface (UI)
3. Providing a degree of hardware independence
4. Managing the system memory
5. Managing the CPU in processing tasks
6. Providing networking capabilities
7. Controlling the access to system resources and
8. Manage the files stored on the hard disk.

The Process & Kernel

A process or task is an instance of a program in execution. It is the smallest unit of work individually scheduled by an OS. A program is a passive entity, whereas a process is an active entity, with a PC (Program Counter) specifying the next instruction to execute and a set of associated resources. Each multiprogramming OS keeps track of all processes and allocates system resources to them according to policies devised to meet design performance objectives.

Kernel is the core or central part of the operating system that controls the most critical processes. It ties all the components of the OS together and regulates other programs.

Here is a live video Tutorial on Operating Systems.  It includes demonstration of some of the Operating Systems used now-a-days - Mac OS X, Fedora and Windows:

Common Hardware Functions

All application programs perform certain tasks as listed below:

• Get input from keyboard or other input devices
• Retrieve data from disks
• Store data on disks
• Display information on a monitor or printer

Each of these basic functions requires a more detailed set of instructions to complete the particular task. All such functionalities are provided as functions, which contain the set of detailed instructions required by the hardware. A typical OS performs hundreds of such functions, each of which is translated into one or more instructions for the hardware.

User Interface (UI)

A UI allows individuals to access and command the computer system. There are two types of UI: Command-based UI and Graphical User Interface. The early User Interface used in Mainframe and Personal Computer systems was command based.

Command-based OS requires that text commands be given to the computer to perform basic activities. Commands like RENAME and COPY are examples for DOS commands used for renaming and copying the files respectively. On the other hand, GUI based OS provides graphical elements like buttons, frames, pictures and icons to have an interaction with the user.

Hardware Independence

Hardware independence is achieved through the use of API (Application Program Interface). An API is a set of function definitions, which can be used from an application software to avail the services provided by OS.

Programmers can use APIs to create application software without having to understand the inner workings of the OS. Application software makes use of the services available in the OS by making request through the API. The following figure depicts how API links the application software to the OS:

Fig. 3: Use of API in application software

Suppose a computer manufacturer designs a new hardware that can operate much faster than the previous one and the same OS for which an application was developed can run on the new hardware, minimal changes are needed to the application to enable it to run on the new hardware. This in-dependency of application on hardware on which it runs is achieved only through API.

How Operating System Works - Presentation

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Organization of a Digital Computer

BASIC COMPUTER ORGANIZATION! 

• We might be using computers for various applications. 
• Generally, computers perform five basic operations namely: input, storage, processing, output and control. 
• A typical computer must get the input from its user, store it temporarily or permanently in a memory device, and process the data to produce information as output. 
• It must also control the activities performed by its various operational units.

Input:

• Computers receive data from its users. End users feed data (e.g., reservation details) to a computer through devices such as keyboard and mouse, called input devices. 
• The given data are then processed by applying a set of instructions, called program.
• Programs instruct the computer what to do with the data.

Storage:Storage:

• The data/program, which are given as input to the computer are stored either in main memory or secondary memory called hard disk. 
• The Processing Unit (CPU) gets the data/instructions from the storage unit whenever required. 

Process :

• Arithmetic and Logical Unit (ALU) processes (analyzes) the data available in the storage unit in order to produce useful information. 
• For instance, it may process the request for booking a seat in a particular train on a particular date if a seat is available on the requested date.
• ALU is the main unit of execution, which performs operations such as arithmetic and logical operations on data.

Output: 

• After processing the input, the computer provides the required information (result) to the user. 
• For instance, in a reservation system, the output may be a printed ticket or display of some information like no. of seats available on a particular date.
• Commonly used output devices are monitor, printer and plotter.

Control: Control: 

• All computers have a control unit that controls the manner in which the sequence of operations occur inside the CPU. 
• The control unit and the ALU form the Central Processing Unit (CPU) of a system. 

Fig. : Functional Organization of a Computer

The various building blocks of a computer are explained below:

Input Unit

• Input unit consists of devices such as keyboard and mouse, with the help of which inputs are given to a computer. 
• Keyboard is the commonly used input device.
• Other input devices are mouse, scanner, light pen etc. Regardless of the type of input device, all input devices perform the following functions:

1. Accept input from the outside world.
2. Convert the input to a form that computer can understand.
3. Supply the converted data to the CPU for further processing.

Storage Unit

• The storage unit consists of a set of storage devices that store data temporarily or permanently for later use. 
•  For instance, one may like to save a business letter for later reference. 
• The storage devices used in a computer system are classified into two categories – primary storage and secondary storage.

Primary Storage:

• The primary storage (also called as main memory) stores and retrieves information very fast. 
• This storage device is generally used to hold programs and data, which are being processed currently by the CPU. 
• It also holds the data being received from the input unit and the intermediate and final results of the program being executed. 
• This memory is volatile in nature, and hence it looses its contents when the power goes off.

Secondary Storage:

• The secondary memory is used like an archive that can hold data and instructions permanently. 
• The program to be executed by CPU is first transferred from the secondary memory to the primary memory before its execution.
• Similarly, after execution, the resultant data are transferred back to the secondary memory for later use.
• The secondary memory is slower and cheaper than the primary memory.
• Examples for secondary memory devices are: floppy diskette, zip diskette, hard disk and magnetic tape.

Output Unit

• Computers store data and instructions internally in binary form. 
• The input given by the user is converted into binary form in order to perform any operation on it. 
• After processing, the binary data must be converted back to the form understood by the user. 
• This task of converting and delivering the required output in human readable form is done with the help of an output device.
• Printer and Video Display Unit (VDU; also called display screen) are commonly used output devices.

Arithmetic-Logic Unit (ALU)

• All calculations are performed in the Arithmetic-Logic Unit (ALU) of the computer. 
• The ALU performs basic operations such as addition, subtraction, multiplication and division. 
• It also performs logical and comparison operations on data.  For instance, comparing one number against another such as checking if one number is less than, equal to or greater than the other number. 
• In order to perform a computation by ALU, the control unit first transfers the required data from the storage unit to ALU and allows ALU to perform the required computation.
• After performing the computation (arithmetic or logical operation), the result is transferred from ALU to the storage unit.

Control Unit

• The control unit controls all other units of a computer. For instance, the input unit does not know where to send the data after it receives input from the user. 
• The control unit gives necessary instructions to the input unit to send the input to the storage unit or to the VDU. 
• In the same way, it controls the flow of data and instructions between the ALU and the storage unit. 
• The control unit also controls what should be sent to the output device and when.

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Evolution of Electronic Computers

GENERATIONS OF COMPUTERS! 

  The early computers, which used vacuum tubes to control the flow of electronic signals, are called First Generation Computers. The computers of this generation are: ENIAC, EDSAC, EDVAC and UNIVAC. These computers used thousands of Vacuum tubes to do the entire operation.

Vacuum Tube is an electronic device that used filaments for producing electronic signals. Its size is about the size of an electric bulb. It produced lot of heat and burn out frequently. Because of the use of Vacuum tubes, first generation computers were too bulky and failed to work too often.

FIRST GENERATION COMPUTERS

The ENIAC (1943-1946), called Electronic Numerical Integrator And Calculator was the first electronic computer. It was completely developed in 1946 by a team led by Eckert and Maucly at the University of Pennsylvania in U.S.A. ENIAC used high-speed vacuum tube switching devices for the control of electronic signals. There were about 19,000 vacuum tubes in ENIAC. It had a very small memory and used wired plug boards as input devices. ENIAC took about 200 µs to add two digits and 2800 µs to multiply. It was primarily designed to calculate the trajectories of missiles.

The computers EDSAC and EDVAC, which were developed after the ENIAC, were called as ‘Stored Program’ computers, because they were designed to store instructions and data internally after the proposal of Von Neumann in the year 1946. His idea was to store machine instructions in the memory of the computer along with data.

EDSAC (1947-1949), abbreviation for Electronic Delay Storage Automatic Computer, was the first stored program computer. It was developed by a team of Scientists led by Prof. Maurice Wilkes at Cambridge University, U.K. This machine used mercury delay lines for storage.

EDVAC (1946-1952) is the abbreviation for Electronic Discrete Variable Automatic Computer (EDVAC) was the first effort made on the concept of Van Neumann. It used binary form (i.e., 0 and 1: called discrete or digital signals) to store data and instructions of the decimal number system used by human beings.

Computers, which operate on discrete or digital signals like 0 and 1, high or low are called Digital Computers, whereas Analog computers operate on analog signals, which are continuously varying in nature. Some of the examples for Analog device are Voltmeter, Ammeter and Speedo meter. EDVAC is an example for Digital computer, which used binary values 0 and 1 for storage and calculation.

Universal Automatic Computer (UNIVAC) was the first computer produced for commercial purpose. It was developed in 1951. It was available for commercial use from 1954.

SECOND GENERATION COMPUTERS

Bardeen, Brattain and Shockley invented transistor in 1947. Transistors are made of Germanium Semiconductor material. Compared to vacuum tubes, transistors were highly reliable, occupied less space and used only one tenth of the power required by tubes.

The computers, which were made of transistors, are called Second Generation computers. They were introduced around 1959 and lasted till 1965. The use of transistors made ‘second’ generation computers faster, smaller and reliable.

Magnetic Core Memory

Memories were also invented during second-generation of computers. Magnetic core memories were made up of magnetic cores, which are tiny rings (0.02 inch diameter) made of ferrite. They are magnetized in either clockwise or anticlockwise direction to represent 0 and 1. This type of memory was used to construct RAM up to the size of 100 KB.

Other Developments

1. Magnetic disk storage was developed during this period.
2. Higher level languages - FORTRAN, COBOL, ALGOL and SNOBAL were introduced.
3. The early operating system called Batch Operating System was developed during this time. For e.g., the Batch OS used in IBM 7000 series computer.
4. Commercial applications like Payroll, Inventory Control, Marketing, Production Planning and General Ledger were rapidly developed.

THIRD GENERATION COMPUTERS

Integrated Circuits (ICs) were used as the switching device in third generation computers. Germanium transistors were replaced with Silicon transistors in the construction of CPU. Because of the use of Silicon transistors in ICs, the switching speed and reliability of CPU increased by a factor of 10. Power dissipation and the size of CPU were decreased by a factor of 10. This resulted in increase in speed of the third generation computers was 1 MIPS. The System/360 introduced by IBM around 1965 was the first third generation computer.

An IC is a small chip consists of electronic components like transistors, resistors and capacitors on a silicon metal plate. The components were integrated together on a silicon material in order to eliminate the wired interconnection between components. The technologies used for the construction of ICs of third generation were SSI and MSI. SSI technology can integrate about 10 transistors in a chip. The integration capacity was increased 10 times in MSI technology to hold up to 100 transistors in one chip.

Other Developments

1. Time-sharing OS like multiprocessing, multiprogramming and multi-user OS were introduced to increase programmer productivity.
2. The High-level language PL/1 of IBM was emerged. Many important on-line systems like dynamic Production control system, Airline reservation system, and Interactive query system were implemented.
3. Significant improvements were made in the design of Core memories. As a result, the size of the main memory reached about 4 MB. Magnetic disk memory was also available up to the size of 100 MB.
4. The standard I O devices keyboard and monitor were newly introduced.

FOURTH GENERATION COMPUTERS

Fourth generation computers used LSI and VLSI technologies for the construction of CPU, memory and supporting chips. The VLSI chip used as the switching device in fourth generation computers is called Microprocessor (P). Introduction of microprocessor as CPU in the fourth generation computer led to the following developments:

1. Extremely powerful Personal Computers (PC) were emerged.
2. Computer cost came down rapidly.
3. Computer’s workload was decentralized. As opposed to a Mainframe computer, which uses a single powerful CPU to be shared by many terminals for many applications, a PC has its own P to do its processing and can be connected in a network.

LSI & VLSI Technologies

In LSI Technology, thousands of components were fit onto one chip, whereas in VLSI technologies, 10 to 50 thousands of transistors were integrated onto a single chip. The ability to fit so much onto an area about half the size of one-rupee coin helped diminish the size and price of computers. The other developments that took place during fourth generation are as follows:

1. Magnetic Core memories were replaced by Semiconductor memories for the construction of RAM. Thus RAM with the size of 16 MB and a cycle time of 200 ns were in common use.
2. Hard disk size for the secondary storage was greatly improved in the order of Giga Bytes. 1 GB of disk on PCs became common in 1994.
3. Optical disks like CD-ROM and DVD-ROM (Digital Versatile Disk ROM) emerged as mass storage devices particularly for read only files. The size of the disk was of the order of 600 MB on a 5.25” disk.
4. High-level languages such as C, C++, ADA and PROLOG were developed. CASE tools were also developed for the Analysis and Design of software.
5. Interactive graphic devices and language interfaces to graphic systems were introduced.

FIFTH GENERATION COMPUTERS

The fifth-generation computers are under development. Fifth generation computers will make use of ULSI chips which consist of millions of components into a single IC. Such computers will use intelligent programming, knowledge-based problem solving techniques, high performance multiprocessor system and improved human-machine interfaces.

The input and output for these computers will be in the form of speech and graphic images. Vision system will be incorporated in order to perceive the surroundings. The computers of this age will be able to understand natural languages like English, Japanese, and Hindi. This will diminish the need for learning computer programming languages by programmers.

Using intelligent programming, the user can tell the computer what to do but not how to do. The computer will do the task of programming itself. The first four generations of computers used Von Neumann’s architecture for the design of digital computers. In Von Neumann architecture, a processor executes simple instructions in a sequence. But the fifth generation computers will use a different design and architecture.

Data flow architecture will be used as the basic design for the construction of fifth generation computers. There will be an extensive use of parallel processing and PROLOG is going to be the language for performing parallel processing. Special coprocessors will be used to make logical inferences and manage massive amounts of stored knowledge. In General, fifth generation computers will be knowledge-based computers.

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How are Computers classified?

CLASSIFICATION OF COMPUTERS! 

Based on the technology used for the construction of CPU in the computers, they are classified as Microcomputers, Mini computers, Mainframe computers and Super computers. Based on the interconnection of computers, we can classify them as distributed computers and parallel computers.

The computers, which use Microprocessors as their CPU, are called Microcomputers. Today most of the computers are of this category. Based on the mode of use, microcomputers are further classified into Personal computers, Portable computers and Workstations.

Personal Computers (PCs)

Personal computers are computers used by individuals for the purpose of running the stand-alone applications like Word Processing, Spread Sheet etc. Data and applications stored in a PC are not available for sharing by other computer users. To make use of the resources available in a PC, it must be connected to a network.

There are two major manufactures of PCs – IBM and APPLE. The machines made by IBM are called IBM PCs. The PCs made by APPLE are called Apple Macintosh. Other manufacturers of PCs also followed the same specifications and design of IBM PCs for the manufacturing of their PCs. The PCs made by third party vendors are known as IBM compatible PCs.

Early PCs designed by IBM had Intel 8088 microprocessors as their CPU. The Operating Systems used by IBM PCs include MS DOS, MS Windows, Windows-NT, UNIX and OS/2. OS/2 is an OS designed specially for IBM PCs.

Apple Macintosh PCs use Apple’s proprietary OS, which was well known for its user friendliness. Apple Macintosh machines started using Motorola 68030 as their microprocessors but later they switched over to Power PC 603 processors.

Portable Computers

Portable computers are smaller in size but more powerful than personal computers. They can be easily carried out by professionals, researchers and entrepreneurs while they are on the road. There are two types of portable computers: Palmtop and Laptop PCs.

Palmtop PCs: Palmtop computers can be held in a palm like a mobile phone kit. Palmtop PCs have a small screen display for both input and output. They can accept handwritten inputs given using electronic pen. A Palmtop PC can also be used as a mobile phone, Fax and email machine. Windows-CE is the OS provided by Microsoft for the operation of Palmtop PCs.

Laptop PCs: Laptop computers are also known as Notebook computers, which can be kept on the lap for working with it. A Laptop PC weighs around 2 Kg and can be carried out easily while traveling. Laptop PCs cost more - at least 3 to 4 times the cost of desktop PCs of the same capacity because of the use of miniature components, which consume low power. They can run on batteries as they have been designed to conserve energy. The configuration of a Laptop PC includes a keyboard, flat screen liquid crystal display, and a Pentium or Power PC processor.

Workstation PC

Workstations are more powerful and more expensive than desktop computers. They can operate at higher speeds – about 10 times faster than PCs. They are generally used by scientists, engineers, and other professionals for handling huge volume of data. They are more suitable for numeric and intensive graphic applications.

The configuration of a typical Workstation includes: a color Video Display Unit (19 inch monitors), 256 MB to 1 GB RAM as main memory and a hard disk of 40-80 GB. Workstations normally use RISC processors such as SUN’s ULTRASPARC, HP’s PA 8500 etc. The OS used by Workstations are UNIX, Linux, SUN Solaris and OS-8.

A system called X Windows is used for Workstations to display the status of multiple processes going on during execution. Most workstations have built-in hardware to connect them to a Local Area Network (LAN).

Mini Computers

Minicomputers, also known as mid range computers were first developed as special-purpose mainframe computers. They were introduced for controlling the machines used in manufacturing industry. However, now they are widely used as general-purpose computers. The most popular minicomputer system is VAM, made by Digital Equipment Corporation (DEC).

Mini computers work well for Distributed Computing Environment (DCE), where the processing power is decentralized and distributed across different computers. An example for distributed computer architecture is Client/Server architecture, in which end users can work with their own microcomputers, and at the same time they can also access and share the resources on the server, which usually is a minicomputer.

Mainframe & Super Computers

Mainframe computers are more powerful than workstations. They are much bigger, faster and more expensive than workstations. Mainframes can process several million-program instructions per second. Organizations like insurance companies, banks, airlines and railways make use of Mainframe computers for handling large number of on-line transactions.

Mainframes can store several Tera bytes of data and transfer data from disk to main memory at several hundred Megabytes/sec. They normally use proprietary operating systems, which usually provide extensive services such as user accounting, file security and control. There are very few manufacturers of mainframe computers, which include IBM and Hitachi.

Supercomputers are the fastest computers available at any given time. They are normally used to solve problems, which require intensive numerical computations. Examples of such problems are: numerical weather prediction, designing supersonic aircrafts, design of drugs and modeling complex molecules. In order to solve such complex problems, many RISC processors are used in the construction of super computers.

The speed of operation of supercomputers is in terms of nanoseconds and even in Pico seconds. Besides arithmetic speed, supercomputers have a large main memory of around 16 GB and a secondary memory of 1000 GB. The speed of data transfer between the secondary memory and the main memory is at least one tenth of the speed of data transfer between main memory and CPU. Such great speed is achieved in super computers through a mechanism called Parallelism.

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Computer and Its Characteristics

INTRODUCTION TO COMPUTERS! 

Computer is a calculating device, which receives input from the user, analyses the input by applying a pre-defined set of instructions to produce output.

For instance, in a ticket reservation system, we enter the details of passenger such as name, age, and gender as well as the date of journey as input. The computer then analyses the given data and makes a reservation.

Data Processing Machine

A computer is also called as a data processor, because it can receive, store, process and retrieve any kind of data. 

For instance, we can use computers to store the details of employees in an organization, which include personal details, pay details, and leave details. 

The stored information can be retrieved and used later to analyze the performance of employees and to print pay slips for them.

Uses of Computers

Computers are everywhere. Every day we come in contact with and use dozens of computers, sometimes without even knowing it. 

When we stop by the ATM to withdraw cash, a computer performs the calculations, updates our account and dispense cash with the help of mechanical parts controlled by it.  

At a supermarket, computers are used to bill the groceries we purchase.  

They can also be used to provide us real-time weather reports; driving directions, etc.   

In modern vehicles, computers can be used to notify emergency response teams if the passengers get caught in an accident.

Two important characteristics of a computer are: speed and accuracy. 

Computers operate at very high speed and execute several million instructions in one second. They also perform their operations with a very high degree of consistent accuracy. 

Because of these features, computers are used in various fields, where there is a need for doing calculations or data processing speedily, accurately and diligently. 

Some of the tasks that can be automated using computers are listed below:

• Preparing documents and performing data processing jobs in offices and homes
• Maintaining accounts and transfer funds in banks
• Preparing salary slips for employees in an office
• Booking tickets in the transportation sector, e.g., Railways, Airlines etc.
• Regulating traffic lights on roads
• Control machines in factories, robotics and modern automobiles
• Design buildings, roads etc.
• Regulating electronic appliances such as Air Conditioners, TVs, VCRs, etc.
• Forecasting weather
• Guiding and operating defense equipment
• Performing scientific and industrial research

Characteristics of Computers

Now-a-days computer is playing a main role in everyday life of human being. 

 It has become the need of people just like television, telephone or other electronic devices at home. 

It is used to solve the problems faced by human problems quickly and accurately. Some of the important characteristics of a computer are described below:

Speed:

A computer is a very high speed electronic device. 

The operations on data stored in a computer are performed using electronic circuits available in a computer. 

The data and instructions flow along these circuits with high speed as fast as the speed of light. 

Moreover, computers can perform millions of operations on data in one second.  

The speed of a computer is usually measured in terms of Mega Hertz (MHz) or Giga hertz (GHz).  Hertz is the standard unit of measuring frequency.  

One Hertz is equal to one cycle per second.  Radio frequencies are usually measured in Kilo Hertz, Mega Hertz, or Giga Hertz.

Solves Arithmetical and Logical Operations

A computer can perform arithmetical and logical operations for solving any problem.  

Arithmetic operations include performing addition, subtraction, multiplication and division on numerical data. 

Logical operation include inclusion, exclusion or negation of values resulted from an arithmetic operation.  It also includes performing comparison on numerical as well as alphabetical data.

Accuracy:

In addition to being very fast, computers operate with high accuracy. 

They produce accurate output provided that the correct input and required set of instructions are given to them.  It means that the output is totally dependant on the given instructions and input data. 

If input data is incorrect then the resultant output will also be incorrect. In computer terminology it is known as garbage-in garbage-out.

Reliability:

The electronic components used in modern computers have very low failure rate. 

A modern computer can perform more complicated calculations without any difficulty and produces consistent (reliable) results.

Storage:

A computer has internal storage (primary) as well as external (secondary) storage. 

In secondary storage, a large amount of data and programs (set of instructions) can be stored for future use. The stored data and programs are available any time for processing.

Retrieves Data and Programs Instantly:

The data and program stored on the storage media can be retrieved quickly in a fraction of a second for further processing.

Automates the Manual Process:

A computer can automatically perform operations without the interference of the user during its execution. 

It controls automatically different devices attached to it. It executes the program instructions one by one sequentially.

Versatility:

Versatile means flexible. Modern computers can perform different kind of tasks one at a time or simultaneously. This is the most important feature of a computer. 

A computer can be used for playing game, and at the same time it can be used for composing and sending emails. 

In colleges and universities, computers are use to deliver lectures to the students.

Channel of Communication:

Today computers are mostly used to exchange messages or data through computer networks all over the world. 

For example, the information can be shared among users of the Internet with the help of a computer.

Diligence:

A computer can continually work for hours together without making any mistake. It does not get tired even after working for long hours.  

It performs various operations with accuracy and speed.

Has No Feelings:

Computer is an electronic machine. It has no feelings. 

It gets connected to the external world on the basis of instructions given to it. 

As a human being, we make decisions based on our feelings, acquired knowledge and prior experience in our daily life. 

But computers cannot make such decision on their own. They decide their path of execution totally based on instructions given to them.

Consistency:

People often gets tired or bored in doing the same task again and again. 

For instance, a teacher may get bored while delivering the same lecture to various groups of students in a class room environment again and again. 

On the contrary, computers can perform doing certain operations consistently (again and again) without loosing its accuracy.

Precision:

Computers are not only fast and consistent but they also perform operations accurately and precisely. 

For example, in manual calculations and rounding fractional values, human beings tend to make mistakes. But, using computer, we  can maintain the accuracy and precision to a great extent.

 

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