Define Structure of MS-DOS Disk in Computer System

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MS-DOS divides the disk which is used by the MS-DOS Operating System to keep track of any vital information about the disk. This system area uses very small portion of the disk, which is about 2% of the total disk capacity. This system area is further divided into:

Define Boot area, Fat area, Root Directory

Boot Area: The boot area, also known as Boot record is the first part of a DOS disk. This area stores a program, which is used to do the task of beginning and loading the MS-DOS Operating System into memory of the computer. This process is called Booting Process. This process starts the MS-DOS by reading the primary part of DOS Program from the disk into the memory. The Booting process can be of two types:
Cold Booty: Which is switching the Power to the Computer System, which enables the computer to start up.
Warm Boot: It is the process adopted, when instead of switching the power on, when the system hangs up, even when the power is on, it is restarted by pressing Alt + Ctrl + Del keys together from the key board it is called warm boot.


FAT Area: FAT stands for File Allocation Table. It is the next part of the system area of the disk. This area of FAT is used by the Ms-DOS to manage the big data portion of the disk. This area is used to record the status of each are of the disk. For managing the area of the disk, the MS-DOS operating system divides the total area into Logical Divisions known as Clusters.
These clusters store the files which contain data. The FAT table consists of numbers, with one place in the table assigned for each cluster on the disk. The number which is recorded in every clusters FAT entry indicates the status of the cluster i.e. is it free or has a file. If these is zero in the clusters FAT entry, it is indicates that the clusters is free and it can be assigned any file. If there is any other number, it indicates that it is in use.

Root Directory  (Dir-Command)


This is the last part of the system area of the disk. This is the file directory, which is basic, but in directory for the disk, which every disk has. The directory records the files that are stored on the disk. This directory has a fixed size for each disk format.
Data Area: It is the bigger part of the disk, where the data files are stored on the disk. Each file on the disk has an entry in the FAT (File Allocation Table) table of the system area. Once a file in the data area is assigned a cluster it finds the entry into FAT table. The data area nearly forms 98% of the disk capacity. The following figure gives the structure of the MS-DOS disk:
Root Directory
File System

System Prompt (Command Prompt)

A system prompt is an indication that the system is ready to take input/instructions from the user and give the output to the user. From the prompt, we give the instructions to the computer. For MS-DOS, if we are using a hard disk computer, when the DOS is fetched into the memory of the computer from the hard disk.
 DOS assumes the default disk drive to bee drive “C”, so it gives an initial system prompt as C>. If any other drive is used to load the DOS into the memory, then it becomes t he prompt. The prompt plays an important role, as it is an indication to start the working on the system. We can change the prompt from the initial system prompt to any other prompt, which we feel.

MS DOS Commands List

These are the instructions which are used to Communicate with the Computer System. We call these instructions as commands as we issue commands to the system, to get our work done. The commands of DOS are divided into two categories, namely:

Internal Commands and External Commands

Internal Commands: These are the commands which are reside in a portion of the computer’s memory and are loaded along with the Operating System into the memory. These commands are always available for execution.
External Commands: These are the commands which have to be loaded from the disk into the memory of the computer before we want to execute them. These commands are usually in the form of files, which reside in the disk, as and when required they will be loaded into Memory before Execution.


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