Introduction to Microsoft DOS

M.S. DOS:

     M.S. DOS stands for Microsoft Disk Operating Systems. MS DOS is the operating system for the IBM’s personal computers and their compatibles. It was released in 1980, when IBM launched its first personal computer. DOS as an operating system has the following features in addition to those which are common to other operating systems.√ Single user operating system√ Hierarchical file structure√ Supports only 80 XXX architecture personal computer√ Memory access limit 640 KB.

DOS Commands:

     DOS contains large number of program files termed as DOS commands. We can use these commands by typing their names on DOS prompt one at a time. These commands given by user tells the computer how to perform a specific job. DOS commands can be classified into two types:

     1)    Internal DOS Commands
 2)   External DOS Commands

Internal DOS Commands:

     Internal DOS commands are those commands which are loaded in the computer system automatically as soon as computer is booted. All these commands are stored in a file called COMMAND.DOS which get loaded at the time of booting.Some of major characteristics of internal commands are:

1)    Memory Resident Commands: These are most commonly used commands which are loaded into the Computer’s memory when DOS is booted.
2)    Fast Access: The fast access is due to their presence in the main memory and so CPU can access it faster than the information stored in the external memory.
3)    If you display the directory, file name of these commands will not be visible, because these form the part of a file called COMMAND.COM.
Examples: COPY, DEL, PATH, DATE, TIME etc.

External DOS Commands:

      External DOS commands are those commands are those commands which are loaded externally in computer system. These commands are not stored in a single file like internal DOS Commands. Each of these commands require a separate executable file.

Some of the major characteristics of external commands are:

     1)    Like conventional program files, these reside on the disk.
2)    To execute these commands, the presence of the corresponding file in the disk is essential.
3)    These files names are displayed when directory is listed.
4)    These files have the extensions .COM or .EXE or .BAT.

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