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Text 1
LOOKING AT HARDWARE
The personal computer is the universal technical system. It is intended for automation, creation, storage, processing and transportation of the data. One of main assignments of a computer is processing and storage of the information. Its configuration can be changed as required.
Your computer is made up of many parts called hardware. Your hardware runs software – programs that translate the instructions you send to your computer into a language it can understand.
The base configuration of a hardware that makes up the most basic computer system includes three devices: a monitor, a keyboard, and a system unit. The most important components placed in a system unit are called internal. The system unit holds your computer’s processor, memory, disk drives, ports, and video card. The external and peripheral units are also connected to a system unit. On appearance system units differ with the form of tank. Tanks can be horizontal (desktop) and vertical (tower).
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PROCESOR AND MEMORY
The central processing unit (CPU) and memory are located on chips inside the system unit. The processor is a main chip of the PC where all calculations are made.
Key parameters of the processor: an operating voltage, a digit capacity, working clock rate, coefficient of an internal clock multiplying, a size of the cache memory.
The processor is connected to other devices of a computer groups by the explorers called as buses. There are three main buses: the address bus, the data bus, the bus of commands.
The CPU is the brain of your computer. This is the place where your computer interprets and processes information. You may have heard computer memory referred to as RAM. The term RAM stands for random access memory. The instructions that your computer gets and the information your computer processes are kept in RAM during your work session.
Your computer’s RAM is not a permanent storage place for information; it is active only when your computer is on. When you turn off your computer, information is deleted from memory. To avoid losing your work, remember to save it on a disk, a permanent storage device, before turning off your computer.
Computer memory is measured in kilobytes or megabytes of information. (A byte is the amount of storage needed to hold one character). One kilobyte equals 1024 bytes, and one megabyte equals 1,048,576 bytes. Software requires a minimum amount of random access memory to work properly. You can usually find memory requirements on software packaging, or you can ask your software dealer.
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MONITOR
Monitor is the device of a visual data representation. This is main output device. Key parameters of the screen monitor are size, frequency of upgrade (regeneration) maps, and a class of protection.
The monitor has a screen that displays information, such as instructions you send to your computer and the information and results your computer sends back after interpreting your instructions. The screen may display information in one color or in several colors.
A color monitor won’t display color unless you have the appropriate video card. A video card fits inside your computer and determines the screen resolution and number of colors your monitor can display. Some video cards enable your monitor to display graphical information, such as geometric designs, in addition to text and numbers.
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KEYBOARD
The keyboard is the key control unit of the PC. It is used for input of the alphanumeric (sign) data, and also commands of handle.
You usе the keyboard to type instructions for your computer, and to type information you want your computer to process. All keyboards have letter keys, punctuation keys, and a spacebar. Most keyboards also have function, numeric, and arrow keys, in addition to ALT, CTRL, DEL, and ENTER or RETURN keys.
Their placement on the keyboard is determined by the computer manufacturer; how they are used is determined by the software you are using.
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Numeric Keypad
Because the number keys are grouped together on the numeric keypad, the keypad is a quick and easy way to type numbers. With many software products, you must press the NUM LOCK key before using the numeric keypad to type numbers. The NUM LOCK key works somewhat like the CAPS LOCK key on your typewriter. When you press the NUM LOCK key on the numeric keypad, the numbers you press on the keypad appear on your screen.
Standard Keyboard
Extended keyboard
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Arrow Keys
In most cases, the arrow keys help you move around the screen. Like other keys, however, their exact function is determined by the software you are using. On standard keyboards, the arrow keys are on the numeric keypad, along with the numbers. To use these keys properly, the NUM LOCK key must not be active. If NUM LOCK is active, you will type a number instead of changing your position on the screen when you use an arrow key.
On extended keyboards, arrow keys appear to the lower left of the numeric keypad. You can use these arrow keys anytime, regardless of whether the NUM LOCK key is active.
Standard Keyboard
Extended keyboard
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Function Keys
Function keys send instructions to the software you are using. For example, suppose you are writing a memo and you have trouble moving a paragraph. By pressing a function key, you may be able to get Help information on your screen.
Like other keys, what a function key does depends on the software you are using. For example, some software uses F1 to display Help information, whereas other software uses the F1 key for a different function (or may not assign a function to that key at all).
The function keys are located across the top on extended keyboards or on the left side of standard keyboard.
Standard Keyboard
Extended keyboard
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ADDITIONAL KEYS
In addition to the standard numeric, arrow, and function keys, extended keyboard include BACKSPACE, INS, DEL, PAGE UP, PAGE DOWN, HOME and END keys. Typically, you can use the PAGE UP, PAGE DOWN, HOME and END keys to move around or scroll through information on your screen, and you can use the BACKSPACE, INS, and DEL keys to edit text. As with other keys on your keyboard, what these keys do depends on the software you are using.
The additional keys on extended keyboard
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ADDITIONAL HARDWARE
In addition to the basic components, most computer systems include other hardware, such as a printer, a mouse, and possibly a modem.
Peripheral devices of the PC are connected to its interfaces and intended for execution of auxiliary operations. Due to them the computer system gains flexibility and scalability.
Scanner is the input device for graphic data. It is intended for input of the graphics information on paper.
Printing stations are used to receive copies of documents on paper. By a principle of operation, distinguish matrix, laser, and ink-jet printers. A printer prints the information processed by your computer. Printers vary in printing speed and output capabilities. For example, some letter–quality printers can print high–quality text quickly; some dot matrix and laser printers can print both text and graphics.
Mouse and special manipulators are the devices of command handle. The mouse is the control unit manipulation type. It can’t be used for input sign information – the principle of handle is clicks of buttons and movements.
By using a mouse, you can move a pointer on your screen. You change the position of the pointer by moving the mouse across your table or desktop. You can also use a mouse to select an item by pointing to it and then clicking a button.
Modem is the device intended for information interchange between remote computers. A modem connects your system to a telephone line so that you can communicate with another computer in another building, or even across the country. You can use a modem to receive business information from services like the Dow Jones News Retrieval and CompuServe Information Service.
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USING DISKS AND DISK DRIVES
A disk is a data storage device consisting of a flat, circular, magnetic surface on which information can be recorded. You will receive several disks with your computer. These already contain information and programs, and are ready to use.
A disk, like a cassette tape, is reusable storage device that holds information, such as software and data, in files. As with random access memory, the amount of space on a disk is measured in bytes. Unlike information stored in random-access memory, however, information stored on a disk is not deleted when you turn off your computer. If you choose to, you can delete the information on a disk, and with proper care, you can use the disk over and over again. Your computer’s disk drives move information stored on the disks into and out of random-access memory. For example, your computer can read software instructions from a disk into random-access memory, and write your data to a disk for safekeeping.
There are two kinds of disk drives: a hard disk drive and floppy disk drive. A hard disk drive contains a non-removable disk that is built in your system. With a hard disk drive, you can store large amounts of information in one convenient place, instead of storing it on many floppy disks.
The hard disk drive can also write and read information to and from your system much faster than a floppy disk drive can write and read information to and from a disk. When your system writes or reads information to or from a disk, the indicator light on the drive goes on.
Each disk drive has a letter assigned to it so you can tell your system where to find instructions and information. For example on many systems the floppy disk drive is called the A drive, and the hard disk drive is called the C drive.
The default drive is the one which operating system uses unless you tell it to do otherwise. It is shown by the prompt that OS displays.
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WHAT IS A COMPUTER?
The term computer is used to describe a device made up of a combination of electronic and electromechanical (part electronic and part mechanical) components. Computer has no intelligence by itself and is referred to as hardware. A computer system is a combination of five elements:
- Hardware
- Software
- People
- Procedures
- Data/information
When one computer system is set up to communicate with another computer system, connectivity becomes the sixth system element. In other words, the manner in which the various individual systems are connected — for example, by phone lines, microwave transmission, or satellite — is an element of the total computer system.
Software is the term used to describe the instructions that tell the hardware how to perform a task. Without software instructions, the hardware doesn't know what to do. People, however, are the most important component of the computer system: they create the computer software instructions and respond to the procedures that those instructions present.
The basic job of the computer is the processing of information. Computers accept information in the form of instruction called a program and characters called data to perform mathematical and logical operations, and then give the results. The data is raw material while information is organized, processed, refined and useful for decision-making. Computer is used to convert data into information. Computer is also used to store information in the digital form.
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HARDWARE
What is hardware? Webster's dictionary gives us the following definition of the hardware — the mechanical, magnetic, electronic, and electrical devices composing a computer system.
Computer hardware can be divided into four categories:
1) input hardware
2) processing hardware
3) storage hardware
4) output hardware.
Input hardware. The purpose of the input hardware is to collect data and convert it into a form suitable for computer processing. The most common input device is a keyboard. It looks very much like a typewriter. The mouse is a hand held device connected to the computer by small cable. As the mouse is rolled across the mouse pad, the cursor moves across the screen. When the cursor reaches the desired location, the user usually pushes a button on the mouse once or twice to signal a menu selection or a command to the computer.
The light pen uses a light sensitive photoelectric cell to signal screen position to the computer. Another type of input hardware is optic-electronic scanner that is used to input graphics as well as typeset characters. Microphone and video camera can be also used to input data into the computer. Electronic cameras are becoming very popular among the consumers for their relatively low price and convenience.
Processing hardware. The purpose of processing hardware is retrieve, interpret and direct the execution of software instructions provided to the computer. The most common components of processing hardware are the Central Processing Unit and main memory.
The Central Processing Unit (CPU) is the brain of the computer. It reads and interprets software instructions and coordinates the processing activities that must take place. The design of the CPU affects the processing power and the speed of the computer, as well as the amount of main memory it can use effectively. With a well-designed CPU in your computer, you can perform highly sophisticated tasks in a very short time.
Memory is the system of component of the computer in which information is stored. There are two types of computer memory: RAM and ROM.
RAM (random access memory) is the volatile computer memory, used for creating loading, and running programs and for manipulating and temporarily storing data.
Chips of a dynamic memory use as the main RAM of a computer. Chips of static memory use as an auxiliary memory (cache memory) intended for optimization of operation of the processor.
ROM (read only memory) is nonvolatile, non-modifiable computer memory, used to hold programmed instructions to the system. The chip of ROM (permanently storage device) is capable to store long time the information, even when the computer is switched off.
BIOS (Basic Input Output System) – main assignment is to check up structure and working capacity of the computer system and provides interaction with keyboard, monitor and hard disk.
The more memory you have in your computer, the more operations you can perform.
Storage hardware. The purpose of storage hardware is to store computer instructions and data in a form that is relatively permanent and retrieve when needed for processing. Storage hardware serves the same basic functions as do office filling systems except that it stores data as electromagnetic signals. The most common ways of storing data are Hard disk, floppy disk and CD-ROM.
Hard disk is a rigid disk coated with magnetic material, for storing programs and relatively large amounts of data.
Floppy disk (diskette) — thin, usually flexible plastic disk coated with magnetic material, for storing computer data and programs. There are two formats for floppy disks: 5.25" and 3.5". 5.25" is not used in modern computer systems because of it relatively large size, flexibility and small capacity. 3.5" disks are formatted 1.4 megabytes and are widely used.
CD-ROM (compact disc read only memory) is a compact disc on which a large amount of digitized read-only data can be stored. CD-ROMs are very popular now because of the growing speed that CD-ROM drives can provide nowadays.
Output hardware. The purpose of output hardware is to provide the user with the means to view information produced by the computer system. Information is output in either hardcopy or soft copy form. Hardcopy output can be held in your .hand, such as paper with text (word or numbers) or graphics printed on it. Soft copy output is displayed on a monitor.
Monitor is a component with a display screen for viewing computer data, television programs, etc.
Printer is a computer output device that produces a paper copy of data or graphics.
Modem is an example of communication hardware — an electronic device that makes possible the transmission of data to or from computer via telephone or other communication lines.
Hardware comes in many configurations, depending on what the computer system is designed to do. Hardware can fill several floors of a large office building or can fit on your lap.
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USING SOFTWARE
Software is the set of programs, procedures, and related documentation associated with a computer system. A program is a coded set of instructions that interprets the information you give to the computer with the keyboard or a mouse, and directs your computer to carry out a task.
Different kinds of software perform different kinds of tasks. Examples kinds of software are operating systems, such as MS-DOS, Windows 95 and its enhanced versions and programs Microsoft Excel and Microsoft Office. There is a wide variety of software programs including word processors, accounting packages, computer-aided design systems and games.
The operating system gets your computer running and controls the operation of your computer's activities. It manages the flow, entry, and display of software and data to and from each part of your computer system. To run a program, you first need to run the operating system. Some years ago the Microsoft disk operating system (MS-DOS) or a computer manufacturer's version of MS-DOS was the operating system most widely used with personal computers. Nowadays it is Windows 98, 2000, XP and others.
When you start a program, you see information on your screen, such as menus and commands. While you are using a program, the operating system is managing your computer's activities. It moves instructions and files from one part of your computer system to another as you choose commands and type information.
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USING FILES AND DIRECTORIES
The information your computer uses is stored on disks in files. A file is a collection of related information such as a computer program or the text of a letter. Each file is given a unique name, and each filename is stored in a directory. To find out about the files in a directory, use the MS-DOS command DIR. The instructions used to run a program are stored in program files, and the information you create by using a program is stored in data files.
As you work with a program, operating system processes the information stored in program files and passes it along to your system when it is needed. When you are finished using the program, your data files are stored on a disk.
When referring to a file, you must use a file specification. This consists of a pathname, a filename and an extension (if there is one).
File extension can be up to three characters long and are used to identify the contents of a file. MS-DOS automatically defines the meaning of some file extensions. Others can be assigned as you wish. For example, .TXT can be used to indicate a text file.
You assign each file a name so that you can identify its contents.
Organizing your files into directories and subdirectories on a disk is like organizing your documents into file folders and then storing them in the drawers of a file cabinet.
Operating system has rules for naming files. It also includes several commands that you can use to work with files.
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Organizing Files into Directories
A disk can hold several hundred or even thousands of files, depending on its size. The more files you have, the more difficult it is to keep track of them. To help you keep track of your files, you can use operating system commands to group your files into directories. MS-DOS lets you organize the files on your disk into directories. Directories are a way of dividing your files into convenient groups. Just as file folders in a file cabinet contain groups of related documents, directories contain groups of related files, such as the minutes and expense reports you create by using a word-processing program. You assign each directory a unique name so that you can identify it.
Using Subdirectories. A directory may contain any number of files, but it is often more convenient to separate the files into subdirectories. When your directories become too large, you can use OS to create additional directories to further organize your files. A directory within another directory is called a subdirectory. This method of organizing the disk is rather like a tree where the files are the leaves of the tree and the directories are the branches. (The first directory is usually called the "ROOT").
You can have more than one file (leaf) with the same name if the files are in different directories.
The organization of directories, subdirectories, and files is called the directory tree. When you format a disk, OS creates one large directory, called the root directory, on the disk. All other directories you create branch out from the root directory.
Each directory has at least two entries, even when otherwise empty. These are ' . ' and ' .. '. The ' . ' specifies the name of the current directory and the '.. ' the name of the parent directory.
OS needs a pathname to find its way to a particular file. The pathname is a series of directory names followed by the required filename, each separated from the last by a backward slash (\). If a file specification does not begin with \ the first part of the specification is taken to be default, or current, directory.
You must tell the computer which directory it must use as its current working directory – that is, the directory you wish to work in.
For example, within your STATUS directory, you could organize your status reports by month if you create a subdirectory for each month. The subdirectory STATUS\JAN would hold the status reports you wrote in January, STATUS\FEB would hold the ones you wrote in February, and so on.
Multilevel Directories. When there is more than one user on your computer, or when you are working on several different projects, the number of files in the directory can become large and unwieldy. To deal with this large number of files, you may want to keep your files separate from a coworker's or organize your programs into convenient categories.
In an office, you can separate and organize files that belong to different people or that relate to specific projects by putting them in different file cabinets. For example, you might put your accounting programs in one file cabinet and your letters in another. You can do the same thing with MS-DOS by putting your files into different directories.
Directories let you group your files in convenient categories. These directories, in turn, may contain other directories (referred to as subdirectories). This organized file structure is called a multilevel directory system.
Note: The maximum number of files or directories that the root directory may contain varies, depending on the type of disk and disk you are using. This maximum capacity for a root directory may vary depending upon how the disk is formatted. The number of subdirectories on a disk is not restricted.
The first level in a multilevel directory is the root directory, which is created automatically when you format a disk and start putting files on it. Within root directory, you can create additional directories and subdirectories.
As you create new directories for groups of files, or for other people using the computer, the directory system grows. Moreover, within each new directory you can add new files or create new subdirectories.
You can move around in the multilevel system by stating at the root and "traveling" through intermediate subdirectories to find a specific file. Conversely, you can start anywhere within the file system and travel toward the root. On the other hand, you can go directly to any directory without traveling through intermediate levels.
The directory that you are in is called the working directory. The filenames and commands discussed in this chapter relate to your working directory and do not apply to any other directories in the structure. When you start your computer, you start out in the working directory. Similarly, when you create a file, you create it in the working directory.
Because you can put files in different directories, you and your coworkers can have files with the same names, but with unrelated content.
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TYPES OF SOFTWARE
A computer to complete a job requires more than just the actual equipment or hardware we see and touch. It requires Software — programs for directing the operation of a computer or electronic data.
Software is the final computer system component. These computer programs instruct the hardware how to conduct processing. The computer is merely a general-purpose machine which requires specific software to perform a given task. Computers can input, calculate, compare, and output data as information. Software determines the order in which these operations are performed.
Programs usually fall in one of two categories: system software and applications software.
System software controls standard internal computer activities. An operating system, for example, is a collection of system programs that aid in the operation of a computer regardless of the application software being used. When a computer is first turned on, one of the systems programs is booted or loaded into the computers memory. This software contains information about memory capacity, the model of the processor, the disk drives to be used, and more. Once the system software is loaded, the applications software can be brought in.
System programs are designed for the specific pieces of hardware. These programs are called drivers and coordinate peripheral hardware and computer activities. User needs to install a specific driver in order to activate a peripheral device. For example, if you intend to buy a printer or a scanner you need to worry in advance about the driver program which, though, commonly goes along with your device. By installing the driver you «teach» your main board to «understand» the newly attached part.
Applications software satisfies your specific need. The developers of application software rely mostly on marketing research strategies trying to do their best to attract more users (buyers) to their software. As the productivity of the hardware has increased greatly in recent years, the programmers nowadays tend to include as much as possible in one program to make software interface look more attractive to the user. These class of programs is the most numerous and perspective from the marketing point of view.
Data communication within and between computers systems is handled by system software. Communications software transfers data from one computer system to another. These programs usually provide users with data security and error checking along with physically transferring data between the two computer's memories. During the past five years the developing electronic network communication has stimulated more and more companies to produce different communication software such as Web-Browsers for Internet.
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OPERATING SYSTEMS
When computers were first introduced in the 1940's and 50's, every program written had to provide instructions that told the computer how to use devices such as the printer, how to store information on a disk, as well as how to perform several other tasks not necessarily related to the program. The additional program instructions for working with hardware devices were very complex, and time-consuming. Programmers soon realized it would be smarter to develop one program that could control the computer's hardware, which others programs could have used when they needed it. With that, the first operating system was born.
Today, operating systems control and manage the use of hardware devices such as the printer or mouse. They also provide disk management by letting you store information in files. The operating system also lets you run programs such as the basic word processor. Lastly, the operating system provides several of its own commands that help you to use the computer.
DOS is the most commonly used PC operating system. DOS is an abbreviation for disk operating system. DOS was developed by a company named Microsoft. MS-DOS is an abbreviation for «Microsoft DOS». When IBM first released the IBM PC in 1981, IBM licensed DOS from Microsoft for use on the PC and called it PC-DOS. From the users’ perspective, PC-DOS and MS-DOS are the same, each providing the same capabilities and commands.
The version of DOS release in 1981 was 1.0. Over the past decade, DOS has undergone several changes. Each time the DOS developers release a new version, they increase the version number.
Windows NT (new technology) is an operating system developed by Microsoft. NT is an enhanced version of the popular Microsoft Windows 3.0, 3.1 programmes. For the best NT performance, you have to use a 486 processor with about 16 Mb or higher. Unlike the Windows, which runs on top of DOS, Windows NT is an operating system itself. However, NT is DOS compatible. The advantage of using NT over Windows is that NT makes better use of the PC's memory management capabilities.
OS/2 is a PC operating system created by IBM. Like NT, OS/2 is DOS compatible and provides a graphical user interface that lets you run programs with a click of a mouse. Also like NT, OS/2 performs best when you are using a powerful system. Many IBM-based PCs are shipped with OS/2 preinstalled.
UNIX is a multi-user operating system that allows multiple users to access the system. Traditionally, UNIX was run on larger computers to which users accessed the systems using terminals and not PC's. UNIX allowed each user to simultaneously run the programs they desired. Unlike NT and OS/2, UNIX is not DOS compatible. Most users would not purchase UNIX for their own use.
Windows 95 & 98 (Windows 2000) are the most popular user-oriented operating systems with a friendly interface and multitasking capabilities. The usage of Windows 95 and its enhanced version Windows 98 is so simple that even little kids learn how to use it very quickly. Windows 95 and 98 are DOS compatible, so all programs written for DOS may work under the new operating system.
Operating system represents the complex of system and auxiliary resources. OS is a support for program supports of higher level – applied and majority of the auxiliary applications.
Basic function of all operation systems is intermediary. It consists in support of several sorts of interface: user interface (between the user and soft-hardware of a computer) hardware-software interface (between program and hardware) program interface (between different sorts software).
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WINDOWS 95
Windows 95 is a new operational system with an easy interface based on the expanding windows principle which uses icons to graphically represent files and their types. Windows 95 makes the way you and your computer interact easy. Most everyday tasks are now easier to accomplish than ever before. For example, the second mouse button has become a powerful weapon. The old Windows 3.0 Program Manager and File Manager have been replaced. The desktop tools that replace them are very like those found on a Macintosh. For example, there is a Recycle Bin that makes it easier to recover accidentally deleted files.
Your computer probably will crash less running Windows 95 than it did with Windows 3.1 and 3.0 or even DOS. Most memory related problems have been removed. Built-in networking features make it easy to reliably share files with co-workers across the room or across the world. And MS-DOS as we know it is so well hidden that you'll rarely give it a thought. Yes, you can still run DOS programs and older Windows applications but most users will probably want to spend most of their time using Windows 95 applications instead.
Microsoft says that it is moving forward to the time when we'll all think more about our data and less about the specific name-brand programs used to create them.
Window 95 plug-and-play capability makes it easy to upgrade your computer hardware. And portable computer users will like what Microsoft has done to make their lives calmer.
A new Windows shortcuts capability makes it easy to reach frequently used files and other necessities. A new Find feature helps you to locate and examine the contents of files in a flash. Most of this is accomplished without sacrificing performance. In fact, many things (like printing) usually happen faster now, due to 32-bit support and other Windows 95 advancements.
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How are directions to be expressed to the computer? The computer is not another human being with whom one can speak easily and clearly in common English. For expressing directions to a computer the programmer in practice uses special programming languages.
Because computers can accept letters and numbers, nearly all the programming languages express the directions in some combination of letters and numbers.
The programming languages in use fall into three general categories in terms of their similarity to ordinary English: machine languages, symbolic languages, and automatic coding languages. In terms of their importance for computer utilization, the machine languages are the most basic, for the computers can use them directly. But symbolic and automatic coding languages are more convenient for the programmer use because they are more similar to English.
Some programming languages are used only with a particular model of computer; some are used with more than one model of computer. For the convenience of the programmer, a language that can be used with several different models of computer is the more useful.
Instructions in a machine language are almost always represented by particular combinations of letters and numbers acceptable to a given computer. Programs written in an appropriate machine language can be directly accepted and used by a computer.
Symbolic languages use symbolic addresses in the operands and usually also are used as the addresses for the instructions. This is in contrast to machine languages, which use absolute addresses. An absolute address is one expressed in machine language. It identifies a specific and physical location of data in storage. An indirect address is an absolute or symbolic address which has as its contents the absolute address (usually) of the operand needed by the instruction. Indirect addresses allow greater flexibility in programming because the programmer by changing the contents of indirect addresses can, in effect, modify a program.
For data description in the symbolic languages, the programmer uses special commands. Being able to use these commands simplifies the process of data description, because often these commands can be used with symbolic addresses as their operands. Thus in many programming languages the programmer can assign addresses in symbolic, relative, or absolute form, depending upon the character of the language and what is most convenient for the programmer at the time.
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HIGH LEVEL PROGRAMMING LANGUAGES FORTRAN
A high level language is a language in which each instruction or statement correspond to several machine code instructions. It is contrasted with a low level language in which each instruction has a single corresponding machine code equivalent. High level languages allow users to write in a notation with which they are familiar, e.g., FORTRAN in mathematical notation, COBOL in English. So, high level languages are oriented to the problem, while low level languages are oriented to the machine code of a computer.
FORTRAN. FORTRAN is an acronym for FORmula TRANslation. It is a problem oriented high level programming language for scientific and mathematical use, in which the source program is written using a combination of algebraic formulae and English statements of a standard but readable form. FORTRAN was the first high level programming language. It was developed in 1954, and was designed to easily express mathematical formulas for computer processing. It is still the most widely used programming language. There were several versions of FORTRAN. The most popular and used was FORTRAN-4.
A FORTRAN program consists of data items, executable statements and non-executable statements. The program is structured in segments which consist of a master segment and optional function segments and subroutines.
Data items in FORTRAN are either variables or constants, and are assigned alphanumeric names by the programmer. Group of similar items of data can be processed as arrays, or tables of data, in which case the individual items are defined by one or more subscripts.
Data items in high level languages may take the following forms:
Integer is a whole number value falling within a range determined by the capacity of the computer being used.
Real is a number expressed in floating-point representation accurate to a number of significant digits, the range again depends on the capabilities of the particular machine being used.
Complex is a number in which two real numbers are used to express the real and imaginary parts.
Logical is a quantity which can only take two values, true or false.
Text is character information, which is not used for mathematical operations.
The actual operations of the program are expressed by means of ‘executable statements’. These can take two forms: ‘assignment statement’ and ‘control statements’. An assigned statement takes the form Variable = Expression. The expression may be either arithmetic or logical. An arithmetic expression can include variables, elements, form arrays, constants and a variety of standard functions which are combined by arithmetic operations, e.g., +, -, * (multiplication), / (division), ** (exponentiation). A logical expression is similar but include the operations AND, NOT, OR, etc, and the logical operators.
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The elements of programming
Most programs are designed to solve a problem. They solve problems by manipulating information or data. As a programmer you do the following:
get the information into the program — input.
have a place to keep it — data.
give the right instructions to manipulate the data— operations.
be able to get the data back out of the program to the user (you, usually) — output.
You can organize your instructions so that
some are executed only when a specific condition (or set of conditions) is True — conditional execution.
others are repeated a number of times — loops.
others are broken off into chunks that can be executed at different locations in your program — subroutines.
These are the seven basic elements of programming: input, data, operations, output, conditional execution, loops, and subroutines. This list is not comprehensive, but it does describe those elements that programs (and programming languages) usually have in common. Many programming languages, including Pascal, have additional features. And when you want to learn a new language quickly, you can find out how that language implements these seven elements, and then build from there. Here's a brief description of each element:
Input. This means reading values in from the keyboard, from a disk, or from an I/O port.
Data. These are constants, variables, and structures, that contain numbers (integer and real), text (characters and strings), or addresses (of variables and structures).
Operations. These assign one value to another, combine values (add, divide, and so forth), and compare values (equal, not equal, and so on).
Output. This means writing information to the screen, to a disk, or to an I/O port.
Conditional execution. This refers to executing a set of instructions if a specified condition is True (and skipping them or executing a different set if it is False) or if a data item has a specified value or range of values.
Loops. These execute a set of instructions some fixed number of times, while some condition is True or until some condition is True.
Subroutines. These are separately named sets of instructions that can be executed anywhere in the program just by referencing the name.
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HIGH LEVEL PROGRAMMING LANGUAGE BASIC & PASCAL
BASIC was developed in 1965 and stands for Beginners All-purpose Symbolic Instruction Code. It is a programming language designed for solving mathematical and business problems. BASIC was originally developed as an interactive programming language for time-sharing on large mainframes. It is widely used on all sizes of computers and has become extremely popular on microcomputers.
There are many different versions of BASIC available with limited versions running on small hand-held computers. BASIC is available in both compiler and interpreter form, the latter form being more popular and easier to use, especially for the first-time programmer. In interpreter form the language is conversational and can be used as a desk calculator. In addition, it is easy to debug a program, since each line of code can be tested one at a time.
BASIC is considered to be one of the easiest programming languages to learn. For simple problems BASIC programs can be written ‘on the fly’, at the terminal. However, complex problems require programming technique, as in any conventional programming language. Since BASIC does not require a structured programming approach, like PASCAL, and since there is no inherent documentation in the language, as in COBOL, BASIC programs can be difficult to decipher later if the program was not coherently designed.
There is no one BASIC language, but something like 90 different versions or dialects; however, all have certain common features that make it easy to use any version once the fundamentals are mastered. Since BASIC is job and human oriented, it cannot be understood by the computer as written, but must go through the intermediate step of a compiler or interpreter. As far as the programmer is concerned, it makes very little difference whether a compiler or interpreter is used.
PASCAL. PASCAL is a general-purpose high level programming language. It is named after the famous French mathematician, Blaise Pascal, who in 1642 designed and built the first mechanical calculator, the “Pascaline”. PASCAL is noted for its simplicity and structured programming design. It is available as both a compiler and an interpreter.
PASCAL was proposed and defined in 1971, and gained popularity in universities and colleges in Europe and the United States. It was later revised and appeared as standard PASCAL in 1975. Its principal features are on teaching programming and on the efficient implementation of the language.
PASCAL may be considered a successor to ALGOL-60, from which it inherits syntactic appearances. The novelties of PASCAL lie mainly in extensive data structuring facilities such as record, set and file structures. It also affords more sophisticated control structures suitable to structured programming.
An algorithm of a computer program consists of two essential parts: a description of actions which are to be performed, and a description of the data, which are manipulated by these actions. Actions are described by statements, and data are described by declarations and definitions.
The program is divided into a heading and a body, called a block. The heading gives the program a name and lists its parameters. These are file variables and represent the arguments and results of the computation. The file output is a compulsory parameter. The block consists of six sections. They are: label declaration part, constant definition part, type definition part, variable declaration part, procedure and function declaration part, and statement part.
The first section lists all labels defined in this block. The second section introduces identifiers for constants. The third section contains type declarations, and the fourth – variable definitions. The fifth section defines procedures and functions. And the last, the sixth, gives the statements which specify the actions to be taken.
The statements used in PASCAL may be: EMPTY statement, GOTO statement, structured statement, compound statement, conditional statement, repetitive statement, WITH statement, etc.
Program structure. In Standard Pascal, programs adhere to a rigid format. You do not have to have all five declaration sections — label, const, type, var, and procedures and functions — in every program. But in standard Pascal, if they do appear, they must be in that order and each section can appear only once. The declaration section is followed by any procedures and functions you might have, then finally the main body of the program, consisting of some number of statements.
Turbo Pascal gives you tremendous flexibility in your program structure. All it requires is that your program statement (if you have one) be first and that your main program body be last. Between those two, you can have as many declaration sections as you want, in any order you want, with procedures and functions freely mixed in. But identifiers must be defined before they are used, or else a compile-time error will occur.
Procedure and function structure. As mentioned earlier, procedures and functions — known collectively as subprograms — appear anywhere before the main body of the program.
Functions look just like procedures except that a function declaration starts with a function header and ends with a data type for the return value of the function.
As you can see, there are only two differences between this and regular program structure: Procedures or functions start with a procedure or function header instead of a program header, and they end with a semicolon instead of a period. A procedure or function can have its own constants, data types, and variables, and even its own procedures and functions. What's more, all these items can only be used with the procedure or function in which they are declared.
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C LANGUAGE
C programming language singles out minimalism. The authors of the language like to program on it easily compiled with the help of one-pass compiler to each elementary component of the program after compiling corresponded to a very small number of machine instructions, and the use of the basic elements of the language is not activated the runtime library. Single-pass compiler compiles the program, not coming back, to the already processed by the text. Therefore, the use of functions and variables must be preceded by their announcement. Code in C it is easy to write on a low level of abstraction, almost like in assembly language. Sometimes C called "universal assembler" or "high-level assembler", which reflects the difference between the languages of the assembly language for the different platforms, and the unity of the standard C code which can be compiled without changes on virtually any model of the computer. C is often called the language of the middle level or even low level, given how close it works to real devices. However, in a strict classification, it is a higher level language.
Compilers of C are developed relatively easy thanks to the simplicity of the language and the small size of the standard library. That is why this language is available on various platforms (it is possible, the range of these platforms are greater than that of any other existing language). Besides, in spite of its low-level nature, the language allows you to create portable programs and supports in this programmer. Standard language program can be compiled on different computers.
C (as well as UNIX, with which it has long been connected) was created by programmers for programmers, the range of which would be slightly wider range of developers of the language. Despite this, the area of use of the language is much broader tasks of the system programming.
C was created with one important purpose: to make more simple writing large programs with a minimum of errors according to the rules of a procedural programming, not adding the final code of the programs of extra overhead for the compiler, as it always make the languages of a high level, such as Basic. On this side of C have the following important features:
- simple language base from which placed in the library of the many significant opportunities, like mathematical functions or functions file management;
- orientation to procedural programming, provides the ease of use of the structural style of programming;
- type system, protects from the senseless operations;
- the use of the preprocessor to, for example, macro definitions and the inclusion of files with the source code;
- direct access to the computer's memory through the use of pointers;
- the minimum number of key words;
- transfer parameters to a function by value, not by reference (with the transfer of the link is emulated using pointers);
- pointers to functions and static variables
- action field names;
- structures and unions user - defined collecting data types, which can be manipulated as a unit.
Here are some of the features of other programming languages, which do not have a C:
- automatic memory management;
- support for object-oriented programming (when the first version of C++ generate the code of the program in the C language);
- short;
- nested function (there are compilers for the C language to implement this function, for example the GNU compiler);
- polymorphism of functions and operators;
- built-in support for multitasking and network
- higher order functions
- currying.
After the appearance of the C language was well received, because he could quickly create compilers for new platforms, as well as allow programmers fairly accurately represent, as obligations are being fulfilled their programme. Thanks to this program, written in C, and effective written in many other languages. As a rule, only optimized manually assembler code can work even faster, because it gives full control over the machine, however, the development of modern c compilers together with complication of modern processors narrowed the gap.
One of the consequences of high efficiency and portability of C is that many compilers, interpreters and libraries of other high-level languages are often implemented in the C language.
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INTRODUCTION TO THE WWW AND THE INTERNET
Millions of people around the world use the Internet to search for and retrieve information on all sorts of topics in a wide variety of areas including the arts, business, government, humanities, news, politics and recreation. People communicate through electronic mail (e-mail), discussion groups, chat channels and other means of informational exchange. They share information and make commercial and business transactions. All this activity is possible because tens of thousands of networks are connected to the Internet and exchange information in the same basic ways.
The World Wide Web (WWW) is a part of the Internet. However, it is not a collection of networks. Rather, it is information that is connected or linked together like a web. You access this information through one interface or tool called a Web browser. The number of resources and services that are part of the World Wide Web is growing extremely fast. In 1996, there were more than 20 million users of the WWW, and more than half the information that is transferred across the Internet is accessed through the WWW. By using a computer terminal (hardware) connected to a network, that is a part of the Internet, and by using a program (software) to browse or retrieve information that is a part of the World Wide Web, the people connected to the Internet and World Wide Web through the local providers have access to a variety of information. Each browser provides a graphical interface. You move from place to place, from site to site on the Web by using a mouse to click on a portion of text, icon or region of a map. These items are called hyperlinks or links. Each link you select represents a document, an image, a video clip or an audio file somewhere on the Internet. The user doesn't need to know where it is, the browser follows the link.
All sorts of things are available on the WWW. One can use Internet for recreational purposes. Many TV and radio stations broadcast live on the WWW. Essentially, if something can be put into digital format and stored in a computer, then it's available on the WWW. You can even visit museums, gardens, cities throughout the world, learn foreign languages and meet new friends. Moreover, of course, you can play computer games through WWW, competing with partners from other countries and continents.
Just a little bit of exploring the World Wide Web will show you what a lot of use and fun it is.
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THE INTERNET
The Internet, a global computer network which embraces millions of users all over the world began in the United States in 1969 as a military experiment. It was designed to survive a nuclear war. Information sent over the Internet takes the shortest path available from one computer to another. Because of this, any two computers on the Internet will be able to stay in touch with each other as long as there is a single route between them. This technology is called packet-switching. Owing to this technology, if some computers on the network are knocked out (by a nuclear explosion, for example), information will just route around them. One such packet-switching network which has already survived a war is the Iraqi computer network which was not knocked out during the Gulf War.
Most of the Internet host computers (more than 50 %) are in the United States, while the rest are located in more than 100 other countries. Although the number of host computers can be counted fairly accurately, nobody knows exactly how many people use the Internet, there are millions worldwide, and their number is growing by thousands each month.
The most popular Internet service is e-mail. Most of the people, who have access to the Internet, use the network only for sending and receiving e-mail messages. However, other popular services are available on the Internet: reading USENET News, using the World-Wide Web, telnet, FTP, and Gopher.
In many developing countries, the Internet may provide executives with a reliable alternative to the expensive and unreliable telecommunications systems of these countries. Commercial users can communicate cheaply over the Internet with the rest of the world. When they send e-mail messages, they only have to pay for phone calls to their local service providers, not for calls across their countries or around the world. But who actually pays for sending e-mail messages over the Internet long distances around the world? The answer is very simple: users pay their service provider a monthly or hourly fee. Part of this fee goes towards its costs to connect to a larger service provider and part of the fee received by the larger provider goes to cover its cost of running a worldwide network of wires and wireless stations.
But saving money is only the first step. If people see that they can make money from the Internet, commercial use of this network will drastically increase. For example, some western architecture companies and garment centers already transmit their basic designs and concepts over the Internet into China, where they are reworked and refined by skilled – but inexpensive - Chinese computer-aided-design specialists.
However, some problems remain. The most important is security. When you send an e-mail message to somebody, this message can travel through many different networks and computers. The data is constantly being directed towards its destination by special computers called routers. However, because of this, it is possible to get into any of the computers along the route, intercept and even change the data being sent over the Internet. In spite of the fact that there are many good encoding programs available, nearly all the information being sent over the Internet is transmitted without any form of encoding, i, e. "in the clear". But when it becomes necessary to send important information over the network, these encoding programs may be useful. Sonic American banks and companies even conduct transactions over the Internet. However there are still both commercial and 1 problems which will take time to be resolved.
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MODERN MEANS OF COMMUNICATION AND ELECTRONIC COMMERCE
Connecting many computer networks and using common addressing system, the Internet has been growing rapidly since its creation in 1983, radio, telephone and cable television wires, satellites being used to deliver Internet services. By the mid-1990s the Internet linked millions of computers throughout the world and it is sure to be the most important commercial and popular means of communication nowadays. The original uses of the Internet were electronic mail, file transfer, bulletin boards and remote computer access. Having expanded considerably during the 1990s, the World Wide Web enables users easily to examine the Internet sites and now it is likely to have become the leading informational service of the Internet.
The first electronic transactions are supposed to have been handled in the 1950s due to telex, radio-teletype and telephone. In the following decades various industries elaborated upon the system of electronic data interchange before a simple and independent of any particular machine standard was created. Since the mid-1990s electronic commerce has become one of the most rapidly growing retail sectors involving the use of computer telecommunication networks for maintaining business relationships and selling information, services and commodities. Although e-commerce usually refers only to the trading of goods and services over the Internet, it actually includes broader economic activity such as business-to-consumer and business-to-business commerce as well as internal organizational transactions that support these activities.
A large part of e-commerce was transferred to the Internet after the first graphical "browser" software for the access to the World Wide Web had been introduced in 1993 and when the number of companies and individuals using "on-line" had greatly increased. In some fields new Internet retailers such as the Amazon bookseller company seem to have grown up overnight and begun successfully competing with traditional retailers. Most of recently established companies are known to include the electronic commerce in their business as well. For example, the Intel. Corporation sold almost half of its chips in the annual computer sales directly through its Web site in 1999 and is planning to move all of its sales to the Web by the end of 2000.
The further development of secure electronic transfer of sensitive information,1 such as credit card numbers and electronic funds transfer orders, is certainly to be essential to the continued growth of e-commerce. It is often necessary to ensure the encrypting of Web purchase forms, many individuals also usually encrypting their e-mail.
Among other innovations that have contributed to the growth of e-commerce are electronic directories and search systems for finding information on the Web; software agents that act autonomously to allocate goods and services; and special identifying services over the Internet. These intermediary services facilitate the sale of goods (actually delivering the goods in case of information), the rendering of services such as banking, ticket reservations, and stock market transactions, and even the delivery of remote education and entertainment. Specialists consider electronic auction sales and markets to be other rapidly developing parts of e-commerce. The former offer a large variety of goods from computers and electronics to books, recordings, automobiles and real estate, while the latter allow a buyer to choose offers from many sellers. It is interesting that from its establishing in 1995, the world's largest on-line open auction site, eBay, grew to more than 5 million members by 1999.
Businesses often develop private intranets for sharing information and collaborating within the company, these networks usually being isolated from the surrounding Internet by special computer-security systems. Businesses also often rely on extranets which are extensions2 of a company's intranet. Such extranets allow portions of company's internal network to be accessible to collaborating businesses, access to the ones being generally restricted through passwords.
One should mention some more important benefits of e-commerce. Due to its development the role of geographic distance in forming business relationships is being reduced. If you were interested in the beginning of a retail business, it would be relatively inexpensive to start a retail Web site. Some traditional businesses are being replaced by their electronic equivalents or are being made entirely useless. Having published fare information and enabled ticketing directly over the Internet, airlines have greatly decreased the role of traditional agencies. Prices of commodity products are generally lower on the Web and it results not only from the lower costs of doing electronic business but also from the ease of comparison shopping in cyberspace. A new form of collaboration known as a virtual company is flourishing now. This type of company is actually a network of firms, each performing some of the processes needed to manufacture a product or deliver a service.