An Introduction to the computer Unit One of BCA First Semester || Fundamental IT

 

An Introduction to the computer 

Computer is an electronic machine that accepts information, processes it according to the specific instructions, and provides the results as new information.
To begin with, you most understand he impact of computer in the world today; Computers are affecting our lives in one-way or the other. Airlines, telephone and electricity bills, banking, medical diagnoses, and weather forecast…The list of services using computers is almost endless.
You must have noticed that some uses of computers, or applications of computers, have made life much easier for you-your air ticket is now issued in a mater of minutes and your credit card gets processed very fast. However, there is something about the computer that might make your fell a little uneasy. Perhaps, a feeling that is far more intelligent and informed and too complex to operate. You may be surprised to know that the computer can’t perform any task without you. The computer needs to be instructed on exactly what it has to do.
The computer can store and manipulate large quantities of data at very high speed and even though, it can’t think. It can make simple decisions and comparisons. For example, a computer can determine which two numbers is larger or which of two names comes first alphabetically and then act upon that decision. Although the computer can help to solve a wide variety of problems, It is merely a machine and can’t solve problem on its own. It must be provided with instructions is the form of a computer program.
A program is a list of instructions written in a special language that the computer understands. It tells the computer which operations to perform and in what sequence to perform them.
In simply a computer is an electronic device that can accept input ands store data, process it and produce output.

Computer has basically three parts:

Keyboard
System Unit (CPU) Central Processing Unit
Monitor (VDU) Visual Display Unit
A Keyboard is used to enter data, which is nothing but characters and numbers, into the computer. We can compare those keys of the typewriter. A system unit receives this data from the keyboard and holds on to it, until it is needed.
A monitor is like a TV screen where whatever is retrieved from the computer can be displayed.

History of Computer
Computers are developed as a result of man’s search for a faster way to calculate. Computer is very fast because data and instructions are represented as pulses within electronic circuits and they travel at the speed of light. The inventions and ideas of many mathematicians and scientists led to the development of the computer.
The first mechanical calculating machines were invented during the 1600’s. It was in 1642, that liaise Pascal developed the first mechanical calculating machine. The calculating machine could be used for addition and subtraction.
In 1671, Gottfried Leibniz’s a German philosopher and mathematician constructed a calculator that was an improvement on Pascal’s invention. This machine could add, subtract, multiply, divide and extract roots.
In the 1830’s, an Englishman Charles Babbage devised the analytical engine, a kind of calculating machine. The analytical engine used axis and gears to computer values and store them and was designed to be a general purpose device that could be used to perform any mathematical operation automatically. The device includes memory, a central processing unit, input/output, and the use of programming language. All these are key elements in today’s computers. That’s why Babbage is often referred to as the father of the modern day Computer.
Lady Augusta add Lovelace was a mathematician, and a long time supporter of Babbage. Lovelace thought of way to program the machine, so that it would repeat the same set of instructions and carry out instructions, If certain conditions exist. These techniques are till in use today. These techniques are still in use today, to make computer programs more efficient. Because of her work, many consider Lovelace, to be the First programmer.

Computer Generation

First Generation (1943-1958)
The storage media or memory used in the first generation computer was vacuum tube. ENIAC (Electronic Numerical Integrator and Computer) was the first electronic general computer. It used vacuum tubes (18,000) and could do 300 multiplications per second.

Second Generation (1958-1965)
The computers using transistors as storage media were classified as second Generation computers. One transistor could do the task of 1000 vacuum tubes. Second generation computers were relatively smaller than the first generation computers. Computers were much faster and reliable. They had greater computing capacity.

Third Generations (1965-1973)
Third Generation computers were general-purpose computers. In 1964, International Business Machines (IBM) Corporation announced its system 360 family of mainframe computers. They are much faster as they used small chips containing thousands of parts integrated in them. Floppy disks. Hard disk, taps of card were used in this generation of computers. Large scale integration (LSI) about 20,000 transistors.

Fourth Generation (1973- Now)
While third generation computers saw the use of integrated circuits in building computers, the fourth generation is characterized by the increased number of circuits, allows more data to be stored on a memory chip. Lare Scale Integration (LSI) and very large scale integration (VLSI), allows memory chips having thousands of storage locations. Fourth generation computers have microprocessor, which have serial numbers. The serial numbers indicates the capability of computer and speed as well.

Fifth Generation

There are three factors that are said to characterize the fifth generation of computers; mega-chip memories, advanced parallel processing, and artificial intelligence. A mega-chip can have more than one million storage locations. With parallel data processing thousands of instructions can be processed simultaneously. Fifth generation computers are expected to have artificial intelligence.

The Personal Computer
The most popular form of the computer in use today is probably the PC or the personal Computer. The PC can be used for various applications. In fact, there are million of PCs already used by individuals and organizations. The PC us small in size but capable enough to handle large tasks. It can perform a divers range of functions, from keeping track of household accounts to keeping records of the stores of a large manufacturing company.

Other Computer Systems
The PC is although the most popular computer system, there are other computer system too, which are categorized on the basis of size, cost; and performance.
Before we describe some of these computer systems. It is essential to understand the term, system. A system is a group of integrated parts that have a common purpose of achieving an objective. These parts or components of the PC system will be discussed in detail, later in the course. A popular system is the Mini-Computer, which is a small, general- Purpose computer. It can vary in size from a small desktop model to the size of a small filing cabinet. A typical mini system is more expensive than a PC and surpasses it in storage capacity and speed. While most PCs are oriented towards single users, mini systems are usually designed to simultaneously handle the needs of multiple users,, I.E. more than one person use a mini computer at the same time.
A mainframe is another form of a computer system that is generally more powerful than a typical mini system. Mainframe themselves may very widely in cost and capability. They are used in large organizations for large-scale jobs.
However, there is an overlap between the expensive Mini’s and small Mainframe models in terms of cost and capability. Similarly, there is an overlap between the more powerful PC systems and the Mini Computer.
At the end of the size and capability scales are the Super Computers. There systems are the largest, fastest and the most expensive computers in the world. They are used for complex scientific and defense applications.

Benefits and Limitations of Computers

The fact that computers have made their impact of almost all aspects of life in today’s world can hardly be questioned. The question that you may ask here is how do you benefit from using a computer.

A computer provides three basic benefits:
Speed
Accuracy (Accurate work)
Diligence (care full hard work or toady effort)

Computers work at very high speeds and are much faster than humans. The human equivalent of an average computer would be one million mathematicians working 24 hours a day. A computer rarely makes mistakes. In fact, most computer errors are cusec by human facilities. Unlike human, computers simply do not get bother or tired. The monotony of repetitive works does not affect computer. Unanticipated situation arises, computer will either produce erroneous results or abandon the task altogether. They do not have the potential to work out and alternative solution.

Computer of a PC system -the Hardware.
Now that you know the benefits and limitations of computer. let us move on to identifying each component of the personal computer with which you will be working during the course. The until that resembles a TV screen is called the Monitor, or more commonly VDU, short form for visual Display Unit.
The component that closely resembles a typewriter is called the Keyboard. The box like structure that houses the necessary components to run the system is called the system unit.
The Printer, as the name suggests, is used to print the results of any operation.
The tiny device connected to the system unit through a cord, resembling a tail is called a Mouse. Moving the Mouse produces a corresponding movement of an arrowhead on the VDU.
These devices are collectively known as the Hardware. Thus hardware comprises of all the physical components of a PC system.

How does a computer work ?
Most activities follow the basic principal of Input-Process-Output. Consider an automobile assembly line. The raw materials are forwarded to the assembling unit. This activity constitutes the Input part of the cycle. The process is the actual building of the automobile. There the process acts upon what has been the input and produces the Output, which in this case would be the finished automobile.
Like all other activities, a computer system follows the Input-Output process or I-P-O cycle. This can best illustrate by an example of an airlines reservation. A person who whishes to travel by air between Singapore and New York first has to fill in a request slip. This contains relevant data, I.E., details of name, age, place of destination, etc. The booking clerk keys in the data from the request slip into the computer. The process in this case includes examining the flight number, the date of the journey, the class requested and determining whether seats are available as per the reservation details. The output of this process is some information confirming the booking, if seats are available, otherwise, the computer turning down the request may issue message.
Let us see how each component of the PC system is related to the I-P-O cycle. The data in the request slip is input the input in computer is via the keyboard. Hence, the keyboard is an input device. The processing is performed by a component of the system unit called the Microprocessor. The information reading availability of seats is displayed on the VDU. Hence, the VDU is an Output Device. As mentioned earlier, the term hardware comprises the input and Output Devices along with the system unit.

A closer Look at the Hardware

Keyboard:
The keyboard has already been identified as an input device. This is a component that closely resembles a typewriter console.
While working on the PC using a keyboard, you eill notice a flashing point on the VDU. This is the cursor. When you press a keyboard, a character is displayed at the point where the cursor is flashing and the cursor moves one position forward. The keyboard provides different keys to perform various operations. (Refer below table)

Key	Function
F1-F12 (Function Table)	Used to perform special functions that depend on the software that is being used
Caps lock	Use to execute an instruction or data being keyed in through the keyboard.
Shift	Caps lock off: If pressed simultaneously with a character key, a capitalized alphabet is input. Caps lock on: If reverses the above effect. Also used to input the upper, symbols of keys with two symbols or characters on them.
Ctrl, Alt	Pressed with other keys, they input special message to the computer.
Backspace	Used to erase the characters to the left of the cursor position.
Num-Lock	Used to activate the numeric keys on the numeric keypad.
Cursor Movement Keys	Used to move the cursor in direction indicated
Home, End, Page Up, Page Down	Used to perform special functions, with which you will become familiar during the course.
Insert	Used to insert characters at the current cursor position.
Delete	Used to delete characters at the current cursor position
Esc	Depends on application, usually used to cancel a command.
Print screen	Used to print whatever is displayed on the screen.

Mouse:
A mouse is a small device that is connected to the system unit by means of a long wire. This is another input device, whose movement causes the corresponding movement of a pointer on the screen. It usually has two or three buttons. Using it, the user can select options from the screen.

Visual Display Unit (VDU)
Let us take a closer look at an output device. Data that has been processed needs to be displayed to the user. This is done using the monitor or the VDU. The VDU is similar to a TV screen and can display both text and graphic images. These displays can be either in black & white or color.

Printer:
The output on the VDU can’t be stored for later reference. For a permanent output, you would require a printer that is also a common output device Using the printer, you can obtain the output on the paper. Printer are capable of printing at very high speeds. The printers commonly used with the PC are the coot-matrix printer, the ink-jet printer and the laser printer.

System Unit:
When data is input to a computer, it is processed and an output is produced at the output device. Processing takes place in the system unit. The component of the system unit that is involved in the actual processing is the microprocessor; another component of the system unit is the internal storage.

Internal Storage
Besides the microprocessor, the system unit also contains a storage area where the data is stored before belong actually processed. This storage area is called the internal storage. It is also referred to as primary storage, main memory or Random Access memory (RAM). Internal storage capacities may differ in different PC’s. Typically, a PC will have an internal storage capacity of 640,000 characters or more.
In computer technology, the storage capacity of a PC is measured in terms of bytes. Where one byte can store one character. Character here refers to any alphabet, number or other symbol. Therefore, to tore the ward Computer, 8 bytes would be required, Just as there is a basic unit, gram, and another unit, kilogram to measure weight, there is also byte and kilobyte (KB) to measure storage capacity. One KB is approximately equal to 1000 bytes. Therefore, 1 KB can store approximately 1000 characters. Another common unit of measurement of storage capacity is the megabyte (MB). which is equal to approximately 1000 KB. High Target capacities are measured in terms of Gigabytes (GB). One GB is approximately equal to 1000 MB.

External Storage
Since the internal storage capacity of PC is limited, it places a restriction on how much data can be stored at a time for processing. However, this is not the only draw back, once the PC is switched off, or in case off a power failure, all the data stored in the internal storage is lost. This means that every time you want to work on the PC, you would have to input the data required for processing. External storage is also refereed to as secondary storage.

There are two kinds of external storage media used with a PC, they are:
Floppy Disk
Hard Disk
Another media for external storage is the cartridge tape, It is particularly suitable for storage of large volume of data. Now CD-ROM and Magneto Optical (MO_ disk have also became an important media to tore large volume of data.
Floppy Dist Hard Disk
Also refereed to as diskettes of floppies. Also referred to as the fix disk.
Removable. Suitable for data from one computer to another. Non-removable. It is attached within the system unit.
Made of flexible tiny materiel. Less resistant to damage by heat, dust and accidental twists. Less prone to damage since it is within that system unit and is packed airtight.
The diskettes currently in use have a diameter of 3.5 inches with a storage capacity of 730 KB or 1.44 MB. Can store data in the range of 20 Mg to 40 GB.
Diskettes having a diameter of 5.25 inches and typical storage capacity of 360 KB are also used, slowly being phased out

Comparison between a Diskette and a Hard Disk.

Disk Drive
The disk drive is contained within the system unit. The drive for diskettes is called Diskettes drive while the drive for a hard disk is called the Hard disk drive.

It is important to differentiate between the storage media and storage devices. The diskette and the hard disk on which data is stored are the storage media, the disk drivers are the devices used for reading and writing. Going back to the analogy of the cassette tape recorder mentioned earlier. The cassette tape would be called storage medium while the cassette player is the storage device.

Software

A PC is incapable of performing any task with the hardware alone. It requires instructions that determine whether it will function as desired or not. Like data, instructions are also entered via the keyboard. In computer terminology, a set of instructions is called a program and one or more programs are called software.

Software used on computers may be of different types. Some important classes of software are:

• Application Software
• Compiler Software
• The Operation Software

Application Software

We spoke of computer applications and identified certain areas where computers being used today. Software specially suited for specific applications is now available in the market, for example, software for billing systems, accounting software or software that enables the storage of documents. Such software is called application software since it is designed for a specific application.

Application software that takes care of variety of business and corporate needs can now be bought off the shelf. These are called standard software packages. They are reasonably priced and come on any standard PC.

Two popular standard software packages are Financial Accounting and Inventory control packages.

Though these packages are for very specific applications, there are general application software’s like database management systems (DEMS). spreadsheets and word processors.

A spreadsheet package allows a user to enter number data, specify formula and perform calculations. Graphs can also be generated from the given data. A word processing package converts a PC into a sophisticated typewriting machine. It has the facility to perform spell checks, provide for synonyms, and allow changes or correcting in the document without having to re-type the entire document.

Compiler Software

Consider the case of four persons Rita, Bunu, Buddha Laxmi, Pramod, Amar, Anita who understand and speak English, Hindi, Nepali and Spanish respectively. To be able to understand each other, they would require some person or persons who could translate whatever is spoken into the language that each can understands.

Similarly, since there are so many programs written in different computer languages. The hardware also needs a translator to convert the computer language into a form that it can understand.

The computer only understands a language of electrical signals, called machine language. Software called the compiler converts the computer language into machine language. for example, there is a C complier that converts program written in the C language or machine language.

Operating system Software

Beside the application software and compiler software. There is a third kind of software, called the operating system, which is very important for the working of the PC.

When a user wants to store any data or program, it is stored at a location that is known only to the operating system. Therefore, the operating system performs the task of storage management. The operating system also performs device management. For instance, when a user wants to print information on the printer, or display information on the VDU, He or she does not have to bother about the actual transportation of the information from the internal storage to the VDU or to the printer. The operating system takes care of it.

All application software packages are written in computer language. There are various computer languages like C,C++, Fortran and Pascal, Each language is best suited for a particular application. C and C++ languages are used to develop highly complex software. Fortran is used for scientific application. Each language has its own vocabulary. There are some packages like Fox-Pro, Ms Access and Sybase that are more English like. Thus, even non-computer professionals, like executives and managers who have never studied computer science, cans learn to use these languages. So each language has its own vocabulary, each language differs form the other.

Memory is the name of parts of computer that is use to store data. Programs and data are stored in the memory unit of the CPU during processing. Memory consists of storage locations. Memory is of two forms. Primary storage of main memory is of two types.

• Read only memory (ROM)
• Random access memory (RAM)

There are certain essential functions that the computer must perform when it is switched on.

• ROM:-It is permanently in built into the computer at the time of its production. ROM is also called firmware. It stores a set of instruction and instructs the computer how to work. The user cannot change these instructions. ROM is non-volatile, that is, when computer goes off this instruction is not lost.
• RAM:- It is short-term memory of volatile memory. That is, when the computer is switched ON, the memory, which available to use, is RAM, but when the computer is switched OFF, all the information disappears. RAM is temporary whereas ROM is permanent memory.

So if we have some important pike of work that we would like to keep, we use secondary storage.

Secondary storage allows string large volumes of data. The contents of secondary storage are not lost when the power is turned OFF.

Secondary storage device are: –

• Hard Disk
• Floppy Disk

Hard Disks:- Hard disk is a large capacity, permanent storage area that offers access to the information stored on it. it is just like a long record and is made of smooth metal or molar plastic, which is coated with magnetic material. Kate is stored and retrieved in blocks. The tracks are therefore divided into block size regions called sectors. Typically, 512 bytes per sector are stored. Control data is recorded on the disk to indicate the start and end points of.

Sector. Hard disk is always fixed in the computer and cannot be removed. Huge number of data can be stored in this type of storage media.

Floppy Disk: Floppy disks are magnetically coated disks on which information; both programs and data typed form the keyboard, can be stored and retrieved. Floppy disks are put into and taken out of a disk drive. These are made of Mylar plastic combed which magnetic oxide and are 5.25 and 3.5 inched in diameter.

CD-ROM (Compact disk Read Only Memory)
It is non – erasable disk used for storing computer data.

Internal Computer System
Computer is a group of integrated parts that have the purpose of performing the operations called the program, which being executed qualifies it to be called a system.

Computer system is basically made of input unit, by which data can be give to the computer, Central processing Unit, which does all arithmetic and logic operations, and Out put Unit which displays the result of these processing.

The data and instructions are understood by the main memory of computer where its Central processing Unit (CPU) takes place.

The processing result are displayed on the screen (Monitor) or printed by a printer.

• The output devices are Monitor or Printer.
• The computer set of parts is called computer system.
• Thus, in a computer system, perfect communication exits.
• The main machine consists of primary unit (also called main memory) holds data instructions and result of processing.
• The Arithmetic logic unit (ALU) is used to perform a calculation and make comparisons. (Decision).
• The control unit (CU) co-ordinates flow of data among the various components.

The ALU and CU are together called the central processing unit or (CPU). the CPU is the main and heart combined which the central nervous system of computer.

Inpute Device: Input devices are main types but basically they are meant for presenting the information to the computer in a form understandable to its machine.
Output device: The results of any computer processing have to be communicated to the user. Output devices translate the computer output into a form understandable to the human beings.

Control Unit

The control unit directs all operations inside the computer. It is known as nerve center of the computer because it controls and co-ordinates all hardware operations.

Functions: It is used to transfer data from the input device to the memory output through ALU and also transfer the results from ALU to the memory and into the output device for printing.

Arithmetic Logic Unit: ALU operates on the data available in the main memory and amends them back after processing once again to the main memory.

Functions: It carries out arithmetic operations like addition, subtraction, multiplication and division.

Device Unit Device

  Main Memory

• (Primary Storage)
• RAM & ROM

Hard Disk
Floppy Disk
(Secondary Storage)

Control Processing Unit

It is the brain of the computer, which does the actual work of processing. Every input given to the computer needs to be processed before the actual output. The central processing Unit and its components. The CPU is an important part also called as the heart of the computer, having many more sub-components that are essential and perform discrete functions. Some of the main components in the CPU are discussed below.

1] SWITCH MODE POWER SUPPLY
All computer components require power supply, which the system draws from the AC mains. The internal power supply does the work of converting the AC input 230 volts into DC output of 5 and 12 volts. The internal power supply us normally as AMPS which provides the cable connections through which power is supplied as per the required voltage to the various, other units like the drivers, the mother board, the keyboard etc.

Whenever the CPU is switched ON/OFF, it is the SMPS, which is, switched ON/OFF, as the external switch is a part of the SMPS.

2] EXHAUST FAN
Whenever the computer is switched on, a fan that is part of the SMPS also starts functioning to give a cooling effect inside the SMPS unit.

3] SPEAKER
A small studio speaker is connected to the motherboard and is used to produce sound effect whenever required in various software programs.

4] MOTHERBOARD
One of the major components of the CPU is the Motherboard, which is large board containing a number of small chips and other additional electronic devices or components. The peripheral attachments are connected to the motherboard. The motherboard has important components like the Microprocessor, Clock, Memory RAM and ROM (Chips).

Microprocessor: The entire PC design is based on this chip. It can do all the mathematical calculations, comparisons logical operations and also attending to requests form attachments are connected like printers, restarting computer etc. The must widely used microprocessor used in computers is form Intel Company. They are usually available as 80286, 80386, 80486 and the Pentium chip.

Clock: The time keeping is done by a clock, which provides signals by way of pulses to set up working pace. The speed of the clock is measured on the frequency of these pluses. The unit of measurement is in MHz or on the basic of the number of instructions per second. A quartz crystal is used giving accurate timings.

Memory: The internal or Main Memory is in the form of chips. Here is the actual place where the RAM and ROM are.
Bus: The Microprocessor works on the data stored in the RAM, Additionally the instructions stored in ROM has to be brought into the RAM whenever required, and therefore communication is essential between the microprocessor and the memory chips as well as other found on the motherboard. This requires communication or interaction is accomplished through a set of wires running between the various components. These wires are called as Buses. There are various types of Bus or wires depending upon the information they carry, the two main types are Data Bus, a set of 8 wires approximately for carrying the address or location where the data is to be stored in the memory.

Ports: Input-Output devices like the printer, keyboard, Mouse etc are connected the CPU through sockets called as Ports. The Microprocessor communicates which the external world through the port. In other words they are the inlets and outlets of the microprocessor. The ports are basally of two types parallel and serial. A parallel port is capable of transmitting full byte. I.e. 8 bites are transferred simultaneously at a time, whereas, in case of a serial port eight bits Queue up and are then send through the cable.

DATA REPRESENTATION

Information is handled in the computer by electrical components such as transistors, integrated circuits, semi conductors, and wires, all of which can only indicate two states or conditions. Transistors are either conducting or non-conducting; magnetic materials are either magnetized or no magnetized in one direction or in the opposite direction; a pulse or voltage’s present or not present all information is represented within the computer by the presence or absence of these various signals.

The starting point of computer data-the smallest, most fundamental unit is called the ‘bit’ . The word ‘bit’ is a charming contraction for a longer and clumsier expression. ‘Binary digit’. We’re all familiar with the ten decimal digits, 0 through 9 that are used to express the numbers that we work with. Binary digits, in sort bits are similar, but while there are ten distinct decimal digits, there are only two different bit values, ‘Zero’ and ‘One’ which are written, naturally enough, as ‘0’ and ‘1’

The bits ‘0’ and ‘1’ represent ‘off’ and ‘on’. The bit is the smallest possible chunk of information in the computer. Bits serve as a building block with which we can construct and work with large and more meaningful amount of information. The most important and most interesting collection of bits is the ‘Byte’. a byte is eight bits, taken together as a single unit of computer data. The memory capacity of a computer or the storage capacity of the disk is measured in bytes.
Bits & Bytes

8 bits=1 Byte=1 Character
1 Byte-00110011=8 Bites
1024 bytes=1 Kilo Byte (KB)
1024 KB=1 Mega Byte (MB)
1024 MB =1 Giga Byte (GB)
1024 GB = 1 Tera Byte (TB)

VIRUS

What is virus ?
A Virus is an actively infections, malicious computer program that place copies of itself into other applications and programs, but not data files or documents. The reason why a virus attaches itself to an executable program is in order to perform destructive action. It has to get executed. Thus, it remains dormant until a user runs the application or program to which it is attached.

When a virus-infected program is executed it leads to the infection of all portions of the memory and then infects the files on the disks. So this is how it may lead to infection of a disk on another computer and thereby spreading the virus through the new system leading to a loss of stored information or data.

A computer virus is basically a program written for destructive purpose. It is written in such a way that it can enter the computer without knowledge of the of the machine or the user. It enters the machine through an infected floppy or a program. It has therefore the capability to make prefect couples of itself and cause abnormal functioning of the machine.

Viruses are brain works of intelligent programmers who are well averse with the intricate chip level manipulation of codes Effects of a virus infection-
1) Corrupt files leading to data loss.
2) Increase files sizes.
3) Interference with display on the monitor.
4) Formatting of the Hard Disk thereby destroying data.
5) Destroying the File Allocation Table.
6) Slowing down of the system.
7) Marking good sectors as bad.
8) Frequent hanging of machines.

BOOT-SECTOR OR PARTITION:
Table virus; A boot-sector virus replaces itself for the bootstrap loader and a partition table virus substitutes itself for the master boot program. This makes such various get loaded every time the machine is switched on. When the virus gets loaded into RAM. It goes infecting all the files on the disk. Also to show that the processing of data is going on normally the virus transfers control to the original bootstrap loader so that the booting procedure can take place normally. Some examples of boot sector/partition table viruses are (c) Brain. PC tone and ? Birthday Joshi. Other example are 13th Friday, Alabama, Ping-Pong ball virus (bouncing ball). Dark Avenger, BOXA virus, etc.

MS-DOS 6.22

DISK OPERATING SYSTEM act as an interface between user and the computer. Did operating system the programs that manage the disk operating and memory location. Managing the disk operation involves reading, writhng, searching, and shorting etc. the contents on to, the disk other operating systems are UNIX, XENIX, OS/2 etc.

EVOSUTION OF DOS.
The home computers were very successful in USA and this inspired IBM (international business Machine) to introduce small computers (PC’ s or Personal computers) into the market. They also wanted and operating system for their Pac range. Mr. Bill Gates of Microsoft purchased the copyright of an operating system called Q DOS (Quickly and dirty Operating system), which was developed by Mr. Tim Peterson and used that as a basic for another operating system known as MS-DOS. There was an understanding between Microsoft and IBM and copy of MS-DOS is sold which every IBM computer.

WHAT IS PC-DOS?

PC-DOS and MS-DOS both refer to the same operating system. The only difference is that IBM has manufactured PC-DOS and Microsoft has manufactured MS-DOS.

What is an operating system?

An operating system is a set of software programs, which provide an interface between the user machines.

Function of an operating system

Al memory management whenever any program is executed or any job is run it has be loaded into memory first, But before your program is loaded into memory the CS has to check any memory is free to gibe allocated to your fob and after the execution of your program the allocate memory is freed so that it can be allocated job.

BI CPU Management: The CPU does the actual processing of the jobs or programs. The CPU gets the job or program form the memory and processing. It after processing the job, the cup to the various jobs this function is called kip scheduling.

CI Disk Management: Whenever the users need to retrieve any files form the disk they need not bother about how and where the files are stored. It is the job of the operating system to keep a track of all the file addresses on the disk and retrieves them as and when required.

DI Input/Output Management: The computer system is attached to many peripheral devices like the keyboard, printer, mouse etc. It is OS which performs the task of co-ordination all the input and output devices.

EI User Interface: The machine understands only the language of ‘0’ and ‘1’ and the cannabis that are as a user give to it are in English like language. There has user and the machine to translate the English like commands into machine language and vice versa. It is the Os, which acts a bridge between the user and machine.

Single user and Multi User Operating system

A single user operating system is one, which supports only a single use at one time. Where as a multi-user operating system supports a number if users at one time. Examples, of multi user operating system are Unix, XENIX; the latest versions of does are also multi-use where as the earlier various are single users. File security is required in a multi user operating system.

 

Multi-user operating system is a computer operating system (OS) that allows multiple users on different computers or terminals to access a single system with one OS on it. These programs are often quite complicated and must be able to properly manage the necessary tasks required by the different users connected to it. The users will typically be at terminals or computers that give them access to the system through a network, as well as other machines on the system such as printers.Examples are:

Diagram shows how OS is handling three user through 3 different terminals

• Ubuntu
• macOS
• All linux based OS
• Unix
• IBM AS400
• Windows 10

Single user operating system becomes a mode where the user has a multipurpose computer screen to run the program and the operating system boots into a single super user that controls all the activities. The primary usage for such a system comes whenever the maintenance for several users takes place at the same time on the network servers. Single client mode is a mode in which a multi-user PC is working framework boots into a single super user.

• Windows 95
• MS-Dos
• Windows NT Workstation
• Windows 2000 professional

 

Source: Google