SOME COMPUTER KNOWLEDGE

E-mail

Short for electronic mail, the transmission of messages over communications networks. The messages can be notes entered from the keyboard or electronic files stored on disk. Most mainframes, minicomputers, and computer networks have an e-mail system. Some electronic-mail systems are confined to a single computer system or network, but others have gateways to other computer systems, enabling users to send electronic mail anywhere in the world. Companies that are fully computerized make extensive use of e-mail because it is fast, flexible, and reliable.
Most e-mail systems include a rudimentary text editor for composing messages, but many allow you to edit your messages using any editor you want. You then send the message to the recipient by specifying the recipient's address. You can also send the same message to several users at once. This is called broadcasting.
Sent messages are stored in electronic mailboxes until the recipient fetches them. To see if you have any mail, you may have to check your electronic mailbox periodically, although many systems alert you when mail is received. After reading your mail, you can store it in a text file, forward it to other users, or delete it. Copies of memos can be printed out on a printer if you want a paper copy.
All online services and Internet Service Providers (ISPs) offer e-mail, and most also support gateways so that you can exchange mail with users of other systems. Usually, it takes only a few seconds or minutes for mail to arrive at its destination. This is a particularly effective way to communicate with a group because you can broadcast a message or document to everyone in the group at once.
Although different e-mail systems use different formats, there are some emerging standards that are making it possible for users on all systems to exchange messages. In the PC world, an important e-mail standard is MAPI. The CCITT standards organization has developed the X.400 standard, which attempts to provide a universal way of addressing messages. To date, though, the de facto addressing standard is the one used by the Internet system because almost all e-mail systems have an Internet gateway.

INTERNAL COMMANDS

1. These are those commands which are contained in command.com files of MS-DOS.
2. These are those functions that are built into the command interpreter.
3. There is no need of any external file in computer to read internal MS-DOS command.
4. These commands can be used as long as DOS is running on the system.
5. Internal commands do not vary from system to system.
6. These are ver, time, del, md, cd, copy con, cls, date, vol, ren, copy etc

EXTERNAL COMMANDS

1. These are those commands which are not in-built in MS-DOS.
2. External commands are those which are not included in the interpreter.
3. There is a need of an internal file in the computer to read external MS-DOS command.
4. External command may vary from system to system. This means any two computers with same version of MS-DOS may have same internal commands, but may have different external commands.
5. These are tree, xcopy, diskcopy, more, print etc

High-level language

A programming language such as C, FORTRAN, or Pascal that enables a programmer to write programs that are more or less independent of a particular type of computer. Such languages are considered high-level because they are closer to human languages and further from machine languages. In contrast, assembly languages are considered low-level because they are very close to machine languages.

The main advantage of high-level languages over low-level languages is that they are easier to read, write, and maintain. Ultimately, programs written in a high-level language must be translated into machine language by a compiler or interpreter.

The first high-level programming languages were designed in the 1950s. Now there are dozens of different languages, including Ada, Algol, BASIC, COBOL, C, C++, FORTRAN, LISP, Pascal, and Prolog.

Programming language

A vocabulary and set of grammatical rules for instructing a computer to perform specific tasks. The term programming language usually refers to high-level languages, such as BASIC, C, C++, COBOL, FORTRAN, Ada, and Pascal. Each language has a unique set of keywords (words that it understands) and a special syntax for organizing program instructions.

High-level programming languages, while simple compared to human languages, are more complex than the languages the computer actually understands, called machine languages. Each different type of CPU has its own unique machine language.

Lying between machine languages and high-level languages are languages called assembly languages. Assembly languages are similar to machine languages, but they are much easier to program in because they allow a programmer to substitute names for numbers. Machine languages consist of numbers only.

Lying above high-level languages are languages called fourth-generation languages (usually abbreviated 4GL). 4GLs are far removed from machine languages and represent the class of computer languages closest to human languages.

Regardless of what language you use, you eventually need to convert your program into machine language so that the computer can understand it. There are two ways to do this:

·  compile the program

• interpret the program

See compile and interpreter for more information about these two methods.

The question of which language is best is one that consumes a lot of time and energy among computer professionals. Every language has its strengths and weaknesses. For example, FORTRAN is a particularly good language for processing numerical data, but it does not lend itself very well to organizing large programs. Pascal is very good for writing well-structured and readable programs, but it is not as flexible as the C programming language. C++ embodies powerful object-oriented features, but it is complex and difficult to learn.

The choice of which language to use depends on the type of computer the program is to run on, what sort of program it is, and the expertise of the programmer.

Assembly language

A programming language that is once removed from a computer's machine language. Machine languages consist entirely of numbers and are almost impossible for humans to read and write. Assembly languages have the same structure and set of commands as machine languages, but they enable a programmer to use names instead of numbers.

Each type of CPU has its own machine language and assembly language, so an assembly language program written for one type of CPU won't run on another. In the early days of programming, all programs were written in assembly language. Now, most programs are written in a high-level language such as FORTRAN or C. Programmers still use assembly language when speed is essential or when they need to perform an operation that isn't possible in a high-level language.

Pseudocode

An outline of a program, written in a form that can easily be converted into real programming statements. For example, the pseudocode for a bubble sort routine might be written:

while not at end of list
compare adjacent elements
if second is greater than first
switch them
get next two elements
if elements were switched
repeat for entire list

Pseudocode cannot be compiled nor executed, and there are no real formatting or syntax rules. It is simply one step - an important one - in producing the final code. The benefit of pseudocode is that it enables the programmer to concentrate on the algorithms without worrying about all the syntactic details of a particular programming language. In fact, you can write pseudocode without even knowing what programming language you will use for the final implementation

What is teleconferencing?

Teleconferencing or Internet Teleconferencing means connecting people by a phone, internet phone or video service so they can hold a meeting or share information in real time without needing to be in the same building, city or country.

Teleconferencing is often used to save travel costs or avoid the ‘down time’ of people travelling to a central point to hold a meeting.

The two most popular types of teleconferencing are:

• Audio-based teleconferencing
• Video-based videoconferencing

Audio-based teleconferencing

Advantages

Some of the advantages of teleconferencing include:

• Easy way to bring a number of people together quickly to discuss a topic
• Most teleconferences can be recorded for a record or to send copies to people who could not make the meeting

Disadvantages

One of the downsides of teleconferencing is that you cannot see the facial expressions or body language of other people in the meeting. This means some conversations can be misinterpreted from time to time because body language is a big part of human communication.

Video-based videoconferencing

Advantages

There are some important advantages that video conferencing has over teleconferencing, namely:

• People in the meeting can see each others facial expressions and body language, making meetings almost as effective as meeting face to face
• Most set ups offer some ability for viewing online documents or video during the meeting

Disadvantages

One of the downsides of video conferencing is the extra bandwidth needed to send your picture out and bring the picture of other attendees into your computer.

Configuration file

A file that contains configuration information for a particular program. When the program is executed, it consults the configuration file to see what parameters are in effect. The configuration file for DOS is called CONFIG.SYS. Older versions of the Windows operating system stores configuration information in files with a.INI extension. The two most important configuration files are WIN.INI and SYS.INI. Starting with Windows 95, most configuration information is stored in MIF files and in the Registry

Magnetic disk storage

The most common physical device for storing files is the magnetic disk. Actually, a disk typically contains several rotating disks, or platters. The surfaces of the platters are covered in metal oxide, and read/written by electromagnetic recording heads, rather like those on an audio cassette recorder. There is one head for each surface, and all the heads move together. The disk rotates at around 3600 rpm (or approx 90mph), with the heads floating microscopic distances above the surfaces. Modern disks for workstations typically hold 500MB - 9GB, and cost of the order of £200 - 3000; prices are currently dropping rapidly.

The surface of a platter is organised as a number of concentric tracks. Each track is divided into sectors. The information held in one sector, a block, is the unit of transfer between the disk and primary memory (typically 4K bytes or so). The operating system determines where the blocks for each file are placed.

The time taken to access a particular block consists of:

• Time to move the heads to the right track - the seek time.
• Time waiting for the sector to come round to the head - the latency.
• Time to actually transfer the data - the block transfer time.

All these times are of the order of tens of milliseconds. The seek time and latency are obviously variable, depending on where the required block is relative to the current position of the heads. It's useful to put all the blocks of a file on one track, to minimise seek times and latencies in accessing the file. Likewise, for a larger file, it's a good idea to have it all on the same cylinder (a set of corresponding tracks on different platters). There are many other placement tricks (such as placing heavily used files on the middle tracks so that the average seek time is reduced). However, since files are of very variable size, and can change size dynamically, it's not usually possible to place the blocks optimally.

Object-oriented programming

A type of programming in which programmers define not only the data type of a data structure, but also the types of operations (functions) that can be applied to the data structure. In this way, the data structure becomes an object that includes both data and functions. In addition, programmers can create relationships between one object and another. For example, objects can inherit characteristics from other objects.

One of the principal advantages of object-oriented programming techniques over procedural programming techniques is that they enable programmers to create modules that do not need to be changed when a new type of object is added. A programmer can simply create a new object that inherits many of its features from existing objects. This makes object-oriented programs easier to modify.

To perform object-oriented programming, one needs an object-oriented programming language (OOPL). Java, C++ and Smalltalk are three of the more popular languages, and there are also object-oriented versions of Pascal.

File management system

Also referred to as simply a file system or filesystem. The system that an operating system or program uses to organize and keep track of files. For example, a hierarchical file system is one that uses directories to organize files into a tree structure.

Although the operating system provides its own file management system, you can buy separate file management systems. These systems interact smoothly with the operating system but provide more features, such as improved backup procedures and stricter file protection