There have been six major releases od DOS number 1 to 6 in addition to several minor revisions specified by decimal points. Version 6.2 is the latest version. Each version provides some extra features or commands for use.
            MS-DOS is like a translator between you and your computer. The programs in this operating system allow you to communicate with the computer disk devices and printer allowing you to use these resources to your advantage.
        DOS handles all low level functions of PC like using keyboard and printer and transferring data and programs to and from diskettes. A system is a group of separate pieces working together where:-
1. PC/CPU -Manager
2. Peripheral Devices - video screen (console) key board, disk drives and printers.
3. MS -DOS order PC manager as to how to manage its peripherals.
Device Names:- All peripheral device are give separate technical names which are as under:
1.MS-DOS Reserved Device Name:- CON
What it is:-Keyboard and screen
2.MS-DOS Reserved Device Name:- PRN or LPT 1
What it is:- Printer
3.MS-DOS Reserved Device Name:- A: , B: , C:
What it is:- Disk Drives
4.MS-DOS Reserved Device Name:- AUX or COM 1
What it is:-Communication Drives
          Information moves to and from computer. The purpose of computer is to gather data, organise and modify that data and then output that data in a more desirable from. Data may come from peripherals such as disk or even through phone lines like (MODEM).
            A computer uses pieces of hardware called as devices to receive input and send output.
1.Mouse/Terminal- for input
2. Printer/Screen- for output
3. Disk Drives- both for input/output.
Naming Files:- To differentiate between different files you lable each with its contents. Hence each file on computer has an unique name.
A file name has two parts:-
1. A primary name
2. A secondary name called extension.
            A primary name should be of 8 characters and extension can be of 0-0 characters long. The first name and the extension are jomed with a dot (.) In between them.
Example:  RESULT. PRT
                  where RESULT is a primary name
               .PRT is secondary name (extension)
Rules For Naming Files:- The combination of following characters can be used:-
1. Alphabets A-Z (both capital and ordinary)
2. Digit (0-9)
3. Special characters allowed are: ; . #, $, %, ( ), [ ], -, No other characters are allowed, neither a blank space.
Types of Files:- There are different kinds of files you can create in your computer according to the usage. To differentiate from each files the computer will give an extension to identify different types of files you have created. These files are:
1. Program files often have .EXE, .COM, .BAT extension.
2. The extension .TXT and .ASC are usually used for files that consists of unformatted text.
3. .DOC means a document file and is a formatted text file which was created using word processing software.
4. The .BAK extension means that the file in backup of another file.
5. The .HLP extension means the file contains help information.
6. The extension .SYS is given to system files.
The Files That DOS Automatically Makes:-
A. IO-SYS:- This is a program to handle Input/Output to the peripheral devices. It stays in memory when we run application program.
B. MS DOS-SYS:- This is a program to use the application programs. It consists of special subprograms to make many commonly needed operations for programmers.
C. IO-SYS and MS DOS-SYS:- These files are loaded into computer memory by a special program called a "BOOT RECORD" each time computer starts.
D. COMMAND.COM:- This accepts the commands and run the programs. It also displays the DOS prompt. Here DOS commands are entered with the maximum length of 127 characters including command name and related parameter/options.
Types of commands:- DOS has two types of commands:-
(i). External
(ii). Interned
External commands:- These commands are actually small separate utility programs that accompany the operating system and expand its usefulness. IF DOS is used through a floppy disk, you need to insert the DOS diskette containing these programs into your computers floppg drive before you invoke them.
           External commands are handled by separate programs from MS-DOS diskette. Each program is the mamber of "COM" or "EXE" family. An external command can only be used when MS-DOS is in a drive. Some of the external commands are : DISKCOMP, MODE, SYS, BACKUP, DISK COPY, XCOPY, PRINT, TREE, CHKDSK, RECOVER, FORMAT and RESTORE etc.