There are three basic main steps to carry out any particular computation:
| • | INPUT- The user feeds in, or inputs, his program and data (the data is the information which the program will process to produce the desired results of the computations.) |
| • | PROCESS/EXECUTION- The computer carries out, or executes the program of instructions. |
| • | OUTPUT- The results of the computation are fed back, or output, to the user. |
The tasks that a computer performs can be divided into three categories:
| • | Arithmetic Operations (addition, subtraction, multiplication and division) |
| • | Comparison operations (determining whether a given value is greater than, equal to, or less than another value) |
| • | Storage and retrieval operations (saving a program on any of the disks for further use) |
ANATOMY OF A COMPUTER SYSTEM
HARDWARE
The hardware consists of the actual physical components of a computer. The three basic components of a computer system, which are essentially the same regardless of the type of system, are: a central processing unit, a primary storage unit and peripheral devices.
The Central Processing Unit (CPU), rightly called the “brain” of the computer is composed of: the control unit and arithmetic/logic unit. The control unit controls the activities of the CPU. It does not process or store the data, but instructs the various parts of the computer in performing these tasks. This unit interprets the instructions given by the user and sends out signals to circuits within the CPU to execute these instructions. The control unit also keeps track of all the programs that have already been executed and the ones which remain to be executed. Finally it collects the output and sends it to the output device, like monitor screen or a printer.
The arithmetic/logic unit performs only the mathematical computations like addition, subtraction, multiplication or division and logical operations. A logical operation is performed by instructing the computer to make a comparison and then to take an action based on the result of that comparison.
The Primary Storage
Types of Computer Memory:
Based on the different needs, the memory in computers is classified into two types:
Primary Memory & Secondary Memory
Primary Memory (also referred to as main memory, primary storage or internal storage) The Primary memory is very important to the immediate processing needs of the computer, which means that when the computer is first switched on, there is an immediate requirement of memory, which is supplied by the primary memory. This unit temporarily holds program instruction, data and the intermediate and final results of processing. It consists of various storage locations, each having a unique address and holding a small amount of information. The address allocated to each storage locations allows the computer to locate items that have been stored in the computer’s memory. This type of memory is of two types:
| • | Random Access Memory or RAM |
| • | Read Only Memory or ROM |
RAM - This is the additional memory which is inside the CPU. RAM is called the Temporary Memory of the computer because the data, information or program that is present in the memory either gets overwritten by new data or information gets erased when the computer is switched off.
ROM - The ROM contains programs that are permanently coded by the CPU. The ROM is called so, i.e read only because it cannot be written on by the CPU. Unlike RAM, ROM does not allow anything to be written on it.
Secondary Memory (also called external storage/external memory/storage device/magnetic storage device) is so called because it is found outside the CPU box. The common examples of secondary storage devices are floppy disks, compact disk and hard disk.
The Peripheral Devices
These devices are input devices, output devices, and secondary storage devices. The programs and data that are entered into a computer to be processed are called input. The word data refers to unorganized facts. When this data is processed to some meaningful form, it is called information.
Input devices
These devices are used to enter data into the computer so that it can be processed. Some examples of input devices are a terminal keyboard, a mouse, a graphics tablet, and a light pen.
Output Devices
The device that gives the processed data or information to us is called the output device. Depending on the requirement of the user, the result is displayed on the monitor or a printer.
| • | Monitor: All the data entered from the keyboard, first appears on the small TV called monitor. It is called so because it allows the user of the computer to keep a check on the things that are being typed. Another very important use of this monitor is that after the processing has been completed by the computer the result is obtained and is flashed on the monitor, allowing the user to see the information. Monitors can be Monochrome (having a dark background) or Coloured (can display text and pictures in all colours) |
| • | Printers: The data that has been processed in the computer can be printed on the paper by means of a printer. They are classified on the basis of how they work. If the printer creates an impression of the typed letter on the paper, it is called an impact printer, otherwise it is known as non-impact printer. |
Displaying output on the screen gives the user the result in a convenient readable form; this output is referred to as soft copy. Printing the results on paper is a way of permanently saving the information which can even be used at a later time. This output is called hard copy.
The Secondary storage devices allow programs, data and processing results to be saved on a storage media (such as magnetic tape, floppy diskettes). If it is required to process these items, they can be transferred back into the primary storage unit of the computer. Although it takes more time to access items in secondary storage devices than in main memory, but the main advantage of secondary storage devices over primary ones is that they are less expensive and can store enormous quantities of data.
SOFTWARE
The computer needs written instructions to solve a problem, these instructions must be written in a programming language. These programs and series of programs are referred to as software. These programs are of two types- system programs and application programs. The system programs direct the computer in its own internal operations while the application programs are written to solve user’s problems.
OPERATING SYSTEMS
Operating System is a set of software modules (Program) within a computer system that governs the control of equipment resources such as processors, main memory, secondary memory, I/O devices and files.
Some examples of operating system are DOS, WINDOWS, WINDOWS-XP, etc.
TYPES OF COMPUTERS
DIGITAL, ANALOG & HYBRID COMPUTERS
The automatic, digital computer was invented in 1833 by Charles Babbage (known as the ‘Father of Computers’) A digital computer is so called because it uses a series of digits to represent all types of information. The digits used are called binary digit (0 and 1) also balled bits. In contrast to digital computers, analogue computers use the values of continuously varying physical quantities to represent information. The desirable features of analog and digital machines can be combined to create a Hybrid computing system, which is partly digital and partly analog.
Programs
Refers to the set of instructions that have to be written for the computer so that it is able to process the data to give the desired information. These programs are written by only those Computer Professionals called programmers. These programmers have the required knowledge of how to communicate with the computer. The tool that is used for writing the set of instructions is called a computer language. Working a program is called executing or running the program.
Types of Programs
The operating system contains several types of programs. These are:
| 1. | Supervisor Program: (also called the monitor or executive) is the major component of the operating system. It coordinates the activities of all other parts of the operating system. This program schedules the order of input and output operations. It also sends messages to the computer operator if an error occurs or if the computer requires additional direction. |
| 2. | Job Control Program: A job is a unit of work to be processed by the CPU. Job control commands are used to identify the beginning of a job, the specific program to be executed, the work to be done, and the input/output devices required. The job control program translates the job control commands written by a programmmer into machine language. |
| 3. | Input/Output Management System: When a user-written program requests information to be transferred into or out of main memory, the input/output (I/O) management system oversees and coordinates the process. Input and output devices are assigned to specific programs and information is moved between the devices and memory locations. |
| 4. | Language Translation Programs: A computer can only execute instructions that are in machine language, which consists of 0s and 1s. In order for the computer to use English-like programs such as those written in Pascal, it must use a language translation program. This program translates the English-like program into machine language. There are two types of language translation programs: interpreters and compilers. Compiler, on the other hand, is a program that translates high-level language into absolute code, or sometimes into assembly language. The input to the compiler is a description of an algorithm or program in a problem-oriented language; its output (the object code) is an equivalent description of the algorithm in a machine-oriented language (the source code). |
| 5. | Library Programs: Library programs are user-written or manufacturer-supplied programs and subprograms that are frequently used in other programs. They perform commonly needed tasks. Library programs are stored in a system library and called into main memory when needed. They are then linked together with other programs. |
| 6. | Utility Programs: Utility programs perform specialized functions. Utility programs or routines are pre-written programs to provide procedures commonly required by virtually all applications. For example, a utility program can transfer data from a tape to a disk, to another tape, or to a printer. |
Computer Languages
The languages that are used to communicate with the computer are called computer languages. These computer languages have developed a great deal since they were first used. Their evolution spans about four stages which are referred to as generations.
Each generation has it’s own individual characteristic language.
| • | First Generation Language: This language used for computers consisted of zeroes and ones. All instructions that had to be given consisted of zeroes and ones. This language was also called machine language (also called binary representation). This was used on computers of the first generation, which used vacuum tubes. Data represented in binary form is stored in the computer as a series of “on” and “off” states of electronic devices representing binary digits (or bits) |
| • | Second Generation Language: The chief characteristic of second generation language was assembly language (also referred to as low-level language). In this type of language the programmer uses symbolic names to specify various machine operations; these symbolic names are called mnemonics. Mnemonics are nothing but easy to remember short-cuts to certain complex instructions. The use of these mnemonics makes assembly language programming easier than machine language programming. Another important improvement of Assemble language over machine language is the use of names to represent storage locations, so that the programmer no longer has to know the address of the location in which a particular value is kept. |
| • | Third Generation Language: The languages used in the third generation were very easy to learn and use on the computers. These language do not require the programmer to understand the technical details of internal computer operations. As they were very close to the English languages so they were called high level languages. Example of such languages are Pascal, BASIC, COBOL, FORTRAN, C, C++, etc. |
| • | Fourth Generation Language: These languages are used even today with most computers available. They are popular because they allow a lot of data to be collected, stored and used for extracting various types of information. Such huge collections of data is called a database. Examples of these type of language are dBASE, FoxPro, Oracle and Ingres. |
VIRUS
The term ‘virus’ is used to describe virtually any type of destructive software. Viruses do not affect the hardware of the computer. The viruses can and ‘do’ corrupt data and programs. Computer Viruses are executable computer programs. Like biological viruses, they find and attach themselves to a host. Most viruses stay active in memory until the system is switched off. When we turn off the computer we remove the virus from memory, but not from the file, files or disk it has affected. So, next time we use our computer, the virus program is activated again and attaches itself to more programs.
Typer of Virus
Mainly, there are two main types of virus - Program Virus & Boot Virus
Program Virus must be written for a specific operating system. Boot Virus exploit the inherent features of the computer (rather than operating system) to spread and activate.
Definitions
Virus: A virus is a type of program that can replicate itself by making (possibly modified) copies of itself. The main criterion for classifying a piece of executable code as a virus is that it spreads itself by means of ‘hosts’. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or carrying it on a removable medium. Additionally, viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with worms.
Worm: A worm, however, can spread itself to other computers without needing to be transferred as part of a host. Many personal computers are now connected to the Internet and to local-area networks, facilitating their spread. Today’s viruses may also take advantage of network services such as the World Wide Web, e-mail, and file sharing systems to spread, blurring the line between viruses and worms.
Viruses can infect different types of hosts. The most common targets are executable files that contain application software or parts of the operating system. Viruses have also infected the executable boot sectors of floppy disks, script files of application programs, and documents that can contain macro scripts. Additionally, viruses can infect files in other ways than simply inserting a copy of their code into the code of the host program. For example, a virus can overwrite its host with the virus code, or it can use a trick to ensure that the virus program is executed when the user wants to execute the (unmodified) host program. Viruses have existed for many different operating systems, including MSDOS, Amiga OS, Linux and even Mac OS; however, the vast majority of viruses affect Microsoft Windows.
Spyware: In the field of computing, the term spyware refers to a broad category of malicious software designed to intercept or take partial control of a computer’s operation without the informed consent of that machine’s owner or legitimate user. While the term taken literally suggests software that surreptitiously monitors the user, it has come to refer more broadly to software that subverts the computer’s operation for the benefit of a third party.
Spyware differs from viruses and worms in that it does not usually self-replicate. Like many recent viruses, however, spyware – by design – exploits infected computers for commercial gain. Typical tactics furthering this goal include delivery of unsolicited pop-up advertisements; theft of personal information (including financial information such as credit card numbers); monitoring of Web-browsing activity for marketing purposes; or routing of HTTP requests to advertising sites.
Adware: Adware or advertising-supported software is any software package which automatically plays, displays, or downloads advertising material to a computer after the software is installed on it or while the application is being used.
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