Disk operating system-Part-21 What is DOS and its function?

Disk operating system (DOS)

Dos is a single user operating system designed for personal computers developed in the early nineties of the last century. It has two rich versions of PC-DOS or MS-DOS developed by Microsoft Corporation. Both these versions have the same function. The original difference was the varieties of computers on which it was installed. Microsoft created PC-DOS for IBM, which designed PC-DOS and sold it continuously on their computers.
At the same time, Microsoft marketed MS-DOS and sold their compatible PCs with IBM.

When Microsoft first developed dos, it used a command-line interface. Later versions used both command-line and menu drive interfaces as well as improved memory and disk management.

DOS was once the most used operating system. It is estimated that more than 7 million computers were being used in it. Now dos is not much used because it does not offer graphical user interface (GUI) and it can not be used even with 32 bit PC processors.

We know that an operating system is an interface between a user and a computer system. Therefore the operating system must be loaded into memory itself. Even then, the user can work with the machine through the operating system. The operating system software is stored in the disk, then it is attached to the disk in the main store and main memory where it is lying.

Starting or Butting MS-DOS

When the computer is powered on, a program automatically starts and loads the operating system. Which makes the computer ready to work. This entire process is called booting.
To load DOS into main memory, there are three important files like IO. Have to connect to SYS, MSDOS.SYS and COMMAND.COM. Loading these three files into main memory is called booting. The booting process function is described below.

1:- When the computer turns on it produces a complete series of self-diagnostic tests called POST (Power on Salf Test). The job of the post is to see if your computer’s hardware is working properly. If the computer sees a problem in an element, an error message immediately appears on the screen.

2:- The program that stores the ROM-BIOS and is used to load the operating system, then it starts running. It is then checked whether the DOS files are correct or not. The following is the order to check it.

• A floppy disk is first searched on the drive and if it exists, the DOS is loaded from the floppy drive.
• If the DOS files are not present in the floppy disk drive, then a search is done on the hard disk. If the DOS files are found on the hard disk drive, then the DOS is loaded from there.
• If the DOS files are not found anywhere, then an error message appears on the screen: non-system disk or disk error

3 :- If dos files arrive on a drive, then its first sector (boot secter) is read. This sector stores a small program called bootstrap loader which stores instructions for the voting process. The bootstap loader is then loaded into the main memory and the instructions given are fully run as follows.

• First the Io.SYS file, then the MSDOS.SYS file is loaded into man memory. In addition, some internal tables like process management, memory management and information management are initiated.
• After this a file named CONFIG.SYS is searched in the AC drive from where DOS is loading. This determines whether the computer system is configured as CONFIG.SYS.
• The COMMAND.COM file (which is the command interpreter of DOS) is loaded into main memory.
• A batch file called AUTOEXEC.BAT is found, and if found, all the instructions in it are executed.
• Finally the DOS PROMPT (which is followed by the drive letter mark ‘: >’) is displayed which shows its drive letter from which the DOS is loaded, ie C: > or A: >. Now the drive in which the DOS is loaded becomes the default drive, which means that whatever operation will take place will be under this drive.

Change of disk drives

C: > Size on the prompt screen indicates that the user is currently working on the hard drive. Default drive can be converted from floppy to hard disk and vice versa just by placing a column (:) after the new drive letter and then pressing enter. For example, type working drive from hard drive to floppy drive.
C: > A:

Once the above command is given, the interpreter (command.com) will interpolate the user’s request in Dos and execute the command. The prompt will change when the command is executed.
A: >

But if there is no floppy near the floppy drive then the dos will show an error message as shown below.
Not ready reading drive A
Abort, Retry, Fail?

This problem can be solved by adding a floppy to the drive and typing the character ‘R’. Then Prompt A: > I will change.

Files

The primary unit storage on a computer is called a file. With the help of one file, MS-DOS provides the ability to identify from one collection of information to another. For example, using 1 word processing program, a letter in its own file contains many files in the computer and not all files are created by the user. Some files come with MS DOS while others also come with applications, such as with a word processor.
These files contain code and other information which is necessary for running the computer and for applications.

The name of a file has two parts.
A Primary file name B. Secondary file name or extension name

Primary name cannot be more than 8 characters and secondary file name cannot be more than three tractors. Secondary file names or extensions have a period (.), Followed by three characters. Extensions are optional but they are used only because they tell the subject of the file. For example, all word processor documents can be given an extension .doc.

Every file must have an Aditya name in the same directory. But if the primary name is the same and the secondary name is the difference,You can then store the information as separate files.

Some valid file names are:

• abc.exe
• cuz.cdr
• diamond.pdf
• diamond.com
• diamond.psd

Names of some invalid files:

• diamond exe (should not be empty)
• diamond, cd (not coma)
• diamond <“. pd (special characters like <= are not allowed)

Directories

Because a hard disk can store a lot of data — up to thousands of mega bytes — so a hard disk can store thousands of files. But as the number of users increases, the number of files also increases – so it becomes very difficult to find the complete details of all the disk files.

Dos provides a solution to this problem. Through this, the hard disk is divided into several parts which are called directories. Each directory maintains a different set of its files. Apart from this, entries of entries (entries) can also be kept in sub-directories. By keeping files through such an arrangement, the file system is a coordinate of the tree below called a directory tree.

The Dos system always starts with a directory called root which is marked with flash (). Other directories are divided into branches from the root directory itself – where does the sub directory of the root directory go. To illustrate this, a drawing has been made. In this, three directories A, B, C emerge from the root directory. Out of these, two and two directories come out of A and C which are called sub-directories of A and C.