Tuesday, June 28, 2011

Class IX, COMPUTER, "Computer Software"

Machine Language

Machine language is the only language that a compute understands directly without any translation, it is the binary language. It is the language of 0’s and 1’s . It consists of strings of binary numbers.
The binary codes are very difficult to memorize for human beings that is why a machine language is cumbersome for a user.

Difference Between a High-Level Language and Low-Level Language

High-Level Languages

High-Level language are more suitable for human use than machine languages and enable the programmer to write instructions easily using English words and familiar mathematical symbols. These symbolic languages are called High-Level languages. These high-level languages consist of simple English sentences, which are very easy to understand and memorize for human being.

Low-Level Languages

Both the machine and assembly languages are called Low-Level Languages. An assembly language is one step higher than the machine language in human readability. A machine language consists of totally of numbers and is almost impossible for humans to read. In an assembly language, some of these numbers are replaced by human readable symbols called language for humans and almost of the same efficiency as machine language for computer operations. An assembly language is a combination of mnemonic operation codes and symbolic codes for address.
Assembly language is very difficult but it requires good skills for programming. A program written in an assembly language is translated into a machine language before computer can understand and execute it. A computer program, which translates an assembly language program into its equivalent machine language, is called assembler.
A program can be written in much shorter time and much precisely when a high level language is used. A program written in a high level language can be executed in any computer system, which has a compiler for that programming language.

Operating System

Operating system provides link between the user and the computer. It enables the user to have complete control over the computer system by commands through the keyboard or any other input device. The supervisor part of an operating system resides all the times in the memory (RAM) of the computer after the computer is turned on. An operating system performs the following tasks:
1. Controls basic Input and Output devices.
2. Allocates system resources.
3. Manages storage space
4. Supports application software
5. Maintains security
6. Detects equipment failure
This enables the user to achieve high efficiencies of which the processing systems are capable. Operating systems can be classified as:
1. Single User Operating System
2. Multi-User Operating System

1. Single User Operating System

Single user operating systems are used on individual systems or Personal Computers. These operating systems reside on disks and re called Disk Operating Systems (DOS). Some of the most widely used single user operating systems are :
3. OS/2
4. Windows 95

2. Multi-User Operating System

Multi-User Operating Systems are used for data processing on lrge computer systems. They enhance the potential of computer systems with multiprogramming, multiprocessing and timesharing facilities making them suitable for large organizations. Some of the multi-user operating systems are:
3. Windows NT
4. Windows 2000 Server


DOS stands for “Disk Operating System”. It is a program, which acts as an interface between the user and the computer hardware. DOS allows manipulation of files and programs by interpreting and processing the commands typed by the user.
The DOS software is automatically copied from a floppy disk or the hard drive into the computer’s memory whenever the computer is turned on or booted(made a computer ready to be used by putting in its instructions). DOS is not an application package that you start and then exit when done. This is an operating system runs from the moment you turn the computer on until you turn the machine off. The major tasks the DOS must carry out are:
1. To control input and output devices.
2. To enable user to load and execute program.
3. To maintain an orderly system of data in the disk.

Types of DOS Commands

There are two types of DOS Commands:
1. Internal Commands
2. External Commands

1. Internal Commands

Internal commands are a part of the DOS program COMMAND.COM and are loaded into memory when you boot your computer. These commands are needed to be used most often, although they are not seen when we display the disk directory of filenames on our screen. Some internal DOS commands are:

This command is used to clear the screen of a monitor.
Syntax: CLS

This command is used to display a list of current directly files and subdirectories.
Syntax: DIR[drive:][path][filename][/p][1w]

This command is used to display the current directory or changes in the current (default) directory.
Syntax: CD[drive:][path]

This command is used to deletes one or more specified files from the disk.
Syntax: DEL[drive][path]file name[/p]
e.g. DEL Aslam.Doc

External Commands

External Commands are programs, which exist on the DOS disk or the hard disk. They are run when you type their name on the command line. For example, typing FORMAT at the DOS prompt results in a program called FORMAT.COM being executed.
External Commands are not frequently used and DOS saves valuable memory space by loading them only when required. Some the external commands are:

This command is used to checks the validity of a disk and reports the total space, used and free space on the selected disk.
Syntax: CHKDSK [drive][path][/f][/v]

This command is used to create a bootable drive and installs the main DOS files.
Syntax: SYS[drive:][path]drive2:
e.g. SYS A:

This command is used to display directory structure.
Syntax: TREE[drive:][path][/f][/a]

This commands is used to copy files (except hidden and system files) and directories, including sub directories.
Syntax: XCOPY source [destination][/a|/m][/d:date][/p][/s][/e][/v][/w]
e.g. XCOPY *.*A:

This command is used to delete all files and sub directories in a directory.
Syntax: DELTREE[/Y][pathname]

Booting the System

The term boot or bootstrap, when used with computers, means start or startup. When we boot our computers, we are turning it on and loading the Disk Operating System (DOS) into our computer’s memory. The sequence of events that occur between the time you turn on your computer and the time it is ready for you to issue commands is referred to as the boot process. At the completion of the boot up process the system gives a DOS Prompt as soon as it is ready for operations.

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