Just for GK : About Computer OS DOS for PA/SA Exam

Introduction to DOS

The DOS is an acronym of Disc Operating System. It was the first widely-installed operating system for personal computers which existed before Windows operating system (which you are using in your computer at present). PC-DOS (Personal Computer DOS) is the first personal computer version of DOS. It was developed by Microsoft Corporatin for IBM Computers. Later, Microsoft released another version called MS-DOS (Microsoft Dos). The latest version of MS-DOS is MS-DOS 6.22, released in 1994. People are lazy enough to call these PC-DOS and MS-DOS with the name DOS. So we can say that the DOS is an acronym which describes about MS-DOS / PC-DOS.

We call it as Disk Operating System, because the operation is loaded into system with the help of floppy disk. DOS is a non-graphical and line-oriented command- or menu-driven operating system (no pictures, only commands). Few DOS versions provide menu-driven operating system with a simple interface. Unlike GUII, it does not provide very user-friendly user interface. The DOS prompt to enter a command looks like C:>

Dos is a single-user operating system and it can execute only one application at a time. One of the limitations of DOS is its file naming. DOS's File system restricts file-names to contain 8 characters with an 'extension' containing three characters.This limitation on naming files is also referred to as  "8.3". Today's operating systems (for example, windows, Macintosh and Unix) support up to 256 characters. Another limitation of DOS is, it cannot take advantage of 32-bit architecture because it was designed for 8-bit and 16-bit processors.

Now a days MS-DOS is not commonly used Operating System, but still it can be accessed from windows Operating System.

DOS Operating system mainly consists of 3 files. They are,

1. IO.SYS (Input - Output System File)
2. MSDOS.SYS (Microsoft Disk Operating System File)
3. COMMAND.COM (Contains Only Internal Commands)

Internal and External Commands of DOS :

Internal Commands :

A command that is stored in the system memory and loaded from the command.com are called as  Internal Commands.

Directory Commands : DIR shows all the files & Directories.

MD    Create Directory

CD     Changes Directory

RD    Removes a Directory

Here   is user specified valid name

File Commands :

Copy to

Copies the Source file contents to the Target file.

Del Erases the files

Type Show the contents of a file

Rename Renames the existing file.

External Commands :

External commands are the commands stored separately as .Com files.

• FORMAT : This is used to format a floppy disk, Normally a new floppy is used with format. Ofcourse already used floppy may reused by taking format command.
• Syntax : Format a:/s:q Format a floppy quickly and transfer system files also. 
• CHKDSK : This is check disk command with this a floppy is analyzed for used space, total no.of bytes remaining , sectors, tracks and if any bad sectors/tracks.coc
• This command mainly used to know about any virus.
• Syntax : Chkdsk a:
• DISKCOPY : To copy the contents of one disk to another floppy disk provided both should have same size and capacity.
• DISKCOPY
• SYS : This command is used to transfer the system files to a floppy disk.
• Sys A
• LABEL : This command is used to give name to a floppy disk 
• Label