DOS Interview Questions and Answers

What is DOS?

DOS is an abbreviation for Disk Operating System and refers to the PC operating system. This operating system works as a medium between user and computer system, and between hardware and software too.

It is a character based, single user, single tasking, standalone operating system.

It can perform following task-
1) Management of Hardware and control devices such as keyboard, mouse, monitor, printer and scanner.
2) File system management for managing files and directories.
3) Memory management (storage device) and allocation of memory to various programs.
4) Management of the programs (kernel, UI and API) and their execution.

Many DOS options and / or enhancements are available, including MS-DOS (Microsoft Disk Operating System), FreeDOS and DR-DOS.

What is the DOS commands and explain the internal and external commands?

DOS commands are small programs and instructions that are made to perform a particular task. Every DOS command works differently. It is difficult to work on the computer without these commands. In DOS, there are many types of commands and they are classified into two types -

(1) Internal Commands
(2) External Commands

Internal Commands : These commands enter into computer memory during computer booting and are part of shell. There is no external file in the computer to read internal command.These commands are not in the form of any files, therefore neither they can be viewed nor can be edited or detected.
For example most commonly used internal commands : DIR, MD, CD, TIME, DATE, COPY, COPY CON, TYPE etc.

External Commands : These are commands that are not in-built in DOS and are not part of shell, they are only loaded in memory when they are invoked. These commands are present in the form of files and mostly are in exe, bat and com extensions ,therefore they can be viewed, copied, changed or deleted.
For example most commonly used external commands : XCOPY, FORMAT, COPY, PRINT, SYS, EDIT, TREE, SORT, PROMPT etc.

Describe the 10 DOS commands?

The 10 DOS command are-

1) CD/CHDIR (Change Directory) command is used to displays or change directories in DOS. CHDIR is the alternative name of CD command.
cd ..
cd c:windows

2) CLS (CLRSCR) command is used to clear the contents of the terminal screen or console.

3) COPY command is used to copy complete file from one location to another. It is also used to make copies of existing files.
copy test.bat c:windows
copy *.txt c:

4) DATE command is used to display the system date and prompts the user to enter a new date.
date /t

5) DEL (ERASE) command is used to permanently delete one or more files from the computer.
del test.txt
del *.txt
del *

6) DIR The dir command provides a list of available files in the current and or parent directory.
dir /p
dir /a
dir d*

7) EDIT is a full-screen text editor, which is used to view, create and modify text files.
edit myfile.txt

8) HELP command provides help about DOS commands.
help dir
help date
date /?

9) MOVE command is used to move one or more files or directories from one location to another. It also used to renames the files or directories.
move test.txt d:win
move d* d:win
move test.txt d: ewtest.txt

10) REN command is used to rename files and directories from the original name to a new name. unlike the move command, this command can not be used to rename subdirectories, or rename files across drives and can not specify a new drive or path for the destination of the renamed file.
ren *.txt *.doc
ren test.txt newtest.txt

Tell about networking related DOS commands?

ARP command is used to display and modify the Address Resolution Protocol(ARP) cache, which is a simple mapping of IP addresses to MAC addresses.
ARP is also useful when diagnosing duplicate IP assignment problems.
arp -a

FINGER command allows you to view information about users logged onto a remote computer, that may include their email address, full name, when last time user logged in and read their e-mail etc.
finger -l user@localhost

HOSTNAME command displays the name of the current host.

IPCONFIG command allow you to configure network interfaces and view information about them.This command can be used to verify a network connection as well as to verify your network settings.
ipconfig /all

PATHPING command utility enables a user to find network latency and network loss. Also that provides useful information about network latency and network loss at intermediate hops between a source address and a destination address.

PING command is one of the most commonly used and known command. It allows the user to ping another IP address or computer/host name. It can help to determine whether the network is able to communicate with the network or not.
ping -a

NBTSTAT command displays protocol statistics and current TCP/IP connections.
nbtstat -a

NET command is used to manage, set, view and determine network settings.
net view
net config

NETSTAT command is used to display the TCP/IP network protocol statistics and information.
netstat -a

NSLOOKUP command enables a user to look up an IP address of a domain or host on the network.

ROUTE command enables to view and modify the IP route table of the computer.
route print

TRACERT / TRACEROUTE command helps determine network related issues or slowdowns. It is similar to ping command but can provides details of how a network packet travels and whether it may fail or slow down. It can help to determine the computer, router, switch or other network device which probably causes your network issues.
tracert -d

What is a batch file, give an example?

Batch files are special files with extension bat or cmd, which are often called scripts file that allows us to automate the task. Batch files contains a list of commands that are always executed together and in sequence, because we run the batch file as "command" instead of running each command individually.

We can create a batch file by using any text editor like the Notepad and by entering some lines of commands, and to save the file with an extension BAT or CMD.
To Run a batch file it require double clicking on it and it can also be run via command prompt or the windows start-Run line.

Open the new text file and enter the following text in it and saved the file as "mybat.bat"-

REM This is an example of BAT file output.
REM what we have...

This batch file contains two remarks i.e. "REM" which are used to provide notes or message by either the author or for the user of the file. Everything wrriten between the @ECHO On and off commands is displayed on the screen during the script's execution. After the second remarks/REM, there is a simple DOS "Dir" command which provide the lists the contents of the current directory.

Note that the individual commands or comments are separated by newlines which runs sequentially after double clicking on mybat.bat batch file.

How to run a Batch File?

A batch file can be run in two ways-

By command prompt as command
Double-clicking on the batch file

What is the difference between copy and copy con in DOS?

Copy is used to make a copy of a file. With this command, we can copy or append files with the same name or a new name in the current directory or any other location.
copy a.txt b.txt
copy a.txt c.txt
copy a.txt+b.txt c.txt
copy c.txt d:

Copy con is also called copy console, it is used to write file. We can not use copy con to edit the file. After write in the file, CTRL Z is required to save and exit .
copy con do.bat

@echo off
echo This batch file does absolutly
echo nothing but print this line.

CTRL Z ends the "writing" of the file.

What is chkdsk command?

Chkdsk is an abbreviation for check disk, used to check the status of the file system.

It scans the disk drive and helps in detecting error, repair and retrieval of data from bad sectors.

chkdsk d: / r
chkdsk d: / f
chkdsk *. *

What is AUTOEXEC.BAT file?

Autoexec.bat (Automatic execute batch) is a special plain-text batch file that is executed after system boot.
with this help, we can run commands, programs and batch files automatically at the time of startup or booting of the system, by adding them to this file.

Which is wild card character in DOS?

Wildcards are special characters and symbols that represent one or more characters. Commonly used wildcards are asterisk (*) and question mark (?).

An asterisk (*) is represents one or more characters, and a question mark (?) is represents a single character.

What is the xcopy command in dos?

The XCOPY command is used to copy one or more files and directories, including subdirectories from one location to another location.

xcopy c: est d: est /i
xcopy c: est d:


Config.sys is a configuration file and it is executed during system boot.

It contains commands and instructions to load device drivers, lastdrive, shell, devicehigh, buffers etc. It also used to load programs in memory to manage memory,hardware, keyboard, mouse, printer, and other peripherals.

Config.sys is editable text file and it can be edit in any text-editing program.

After executing the command of the config.sys file, the autoexec.bat file is executed.

How we can create a directory in DOS?

MD or mkdir MS-DOS command can use to create a directory

MKDIR dirname
MD dirname
md d:dirname

Explain the use of help DOS Command?

The help command provides more detailed information about other commands.

HELP [command]
Help dir
Help time

What is the full form of DOS?

The full form of DOS is Disk Operating System. This operating system works as a medium between user and computer system, and between hardware and software too.

Latest Updates

Pipes and Cistern

Three taps A,B and C can fill a tank in 12, 15 and 20 hours respectively. If A is open all the time and B and C are open for one hour each alternatively, the tank will be full in?

Two pipes A and B can fill a tank in 6 hours and 4 hours respectively. If they are opened on alternate hours and if pipe A s opened first, in how many hours, the tank shall be full?

A large tanker can be filled by two pipes A and B in 60 min and 40 min respectively. How many minutes will it take to fill the tanker from empty state if B is used for first half of the time, and A and B fill it together for the other half?

A tank is filled by 3 pipes with uniform flow. The first two pipes operating simultaneously fill the tank in the same time during which the tank is filled by the third pipe alone. The 2nd pipe fills the tank 5 hours faster than first pipe and 4 hours slower than third pipe. The time required by first pipe is?

Two pipes A and B together can fill a cistern in 4 hours. Had they been opened separately, then B would have taken 6 hours more than A to fill the cistern. How much time will be taken by A to fill the cistern separately?

Two pipes A and B can fill a tank in 24 min and 32 min respectively. If both the pipes are opened simultaneously, after how much time B should be closed so that the tank is full in 18 min?

Two pipes A and B can fill a tank in 36 min and 45 min respectively. A water pipe C can empty the tank in 30 min. First A and B are opened. after 7 min, C is also opened. In how much time, the tank is full?

Two pipes can fill a cistern in 14 hours and 16 hours respectively. The pipes are opened simultaneously and it is found that due to leakage in the bottom it took 32 min more to fill the cistern. When the cistern is full, in what time will the leak empty it?

Bucket P has thrice the capacity as Bucket Q. It takes 60 turns for Bucket P to fill the empty drum. How many turns it will take for both the buckets P and Q, having each turn together to fill the empty drum?


In a class , 30 % of the students offered English, 20 % offered Hindi and 10 % offered Both.If a student is offered at random, what is the probability that he has offered English or Hindi?

In a lottery ,there are 10 prizes and 25 blanks.A lottery is drawn at random. what is the probability of getting a prize ?

Two dice are thrown simultaneously .what is the probability of getting two numbers whose product is even?

Two diced are tossed the probability that the total score is a prime number?

Two cards are drawn at random from a pack of 52 cards What is the probability that either both are black or both are queens?

Two dice are thrown together .What is the probability that the sum of the number on the two faces is divisible by 4 or 6?

A bag contains 6 white and 4 black balls .Two balls are drawn at random .Find the probability that they are of the same colour?

In a simultaneous throw of a pair of dice,find the probability of getting a total more than 7?

An unbiased die is tossed.Find the probability of getting a multiple of 3?

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