If you’re a Computer Scientist or Back-End Developer learning about the history of programming and personal computers, then you’ve surely come across the term “DOS” — but what is it exactly? And why do we only hear about DOS when we talk about computers in the ’80s and ’90s?

In this article, we’ll go over what DOS is, how it works, how it was replaced, and why people still use it today.

What is a disk operating system?

A DOS (disk operating system) is a type of operating system that runs from a disk drive rather than a paper-based medium like a punch card. More specifically, DOS refers to an early command-line-based operating system used to access, manage, and control a computer’s hard drive and hardware components such as the processor and memory.

This is different from today’s most popular operating systems, which all use a graphical user interface (GUI) rather than a command line. But, one thing that DOS and GUI-based operating systems have in common is that they’re the key to getting a computer to do what you want it to do. This includes finding a personal document file, connecting to the internet, or running a computationally intensive program.

Life before GUIs

Whether you’re reading this on a device powered by macOS, Windows, Android, iOS, or Linux, you’re working within a GUI-based operating system. That means that you can control and manage your computer or device through visual representations like icons, folders, menus, and files.

But, believe it or not, using a computer wasn’t always this easy or intuitive. Instead, people typed in commands to navigate through files and run applications stored on the computer hard drive.

Here’s how it worked. Suppose that you want to run a program for your next coding project. The program is stored as a script file on your hard drive in a folder (or directory) named Codecademy.

The first thing you might want to do is double-check that the file is there. With DOS, you’d do this by:

1. Typing in a command to navigate to the Codecademy directory.
2. Typing in another command to list all the files in the Codecademy directory.
3. Once you’ve confirmed that your script file is there, you’d type in another command to run your program.

As you might expect, using DOS is a bit like coding. There are specific commands and syntax structures that you need to abide by to get things done.

But, while people using DOS machines needed to learn new languages, it was still a huge improvement on the previous methods of writing and executing commands and computer programs using hundreds or thousands of punch cards.

A DOS by any other name

The term “DOS” refers to the general concept of controlling a computer through a system based on a disk drive. Since the earliest widespread adoption of DOS in the 1980s, several popular DOS-based operating systems have been developed — each with its own name. But as you’ll see, all of these versions of DOS are closely related.

QDOS and 86-DOS

One of the earliest DOS-based operating systems, QDOS (Quick and Dirty Operating System), is also known as 86-DOS. In 1980, Microsoft bought the rights to QDOS/86-DOS to develop a new DOS-based operating system designed to run on IBM’s original personal computer.

PC DOS

When IBM contracted Microsoft to develop an operating system for its new personal computers, Microsoft worked from the QDOS/86-DOS operating system. The result was an IBM-exclusive operating system known as PC DOS.

But, Microsoft never sold PC DOS to IBM but instead licensed it. So, IBM paid Microsoft a fee for every personal computer sold with PC DOS installed, and Microsoft was free to license its DOS software under another brand name. This is how MS-DOS was born.

MS-DOS

When Microsoft licensed its DOS-based operating system to computer manufacturers besides IBM, it was branded as MS-DOS.

While the first IBM personal computers technically ran on MS-DOS, IBM rebranded the operating system as PC DOS. So, PC DOS and MS-DOS essentially refer to the same thing. When most people think of DOS, they think of MS-DOS with its famous C:> starting prompt.

From DOS to GUI

After IBM released its first DOS-based personal computers, the rest was history. Practically overnight, computers were no longer just a highly technical tool for businesses and research institutions but also something that anyone could use at home, work, or school.

And, when the first Apple Macintosh came out in 1984, people saw how computers could be even easier to use with a GUI-based operating system. Microsoft caught up with the release of its first high-quality GUI-based operating system, Windows 95.

While the early versions of Windows ran under DOS, Microsoft eventually developed operating systems that ran independently of MS-DOS, such as Windows 2000 and Windows XP. Since then, MS-DOS has essentially become obsolete.

DOS vs. Unix

Since DOS uses a command-line prompt, you might wonder how it differs from Unix — the operating system that powers Linux and macOS today.

So, when you open the terminal on your Mac, is that DOS? No, it isn’t. Both DOS and Unix were developed independently, and each has its own strengths and weaknesses, such as:

• DOS was initially designed for single-tasking, while Unix has always been able to handle multi-tasking or running multiple programs at once.
• DOS was designed for single users, so it could never handle file ownership and managing user permissions like Unix-based systems.
• DOS was less power-intensive than Unix, which made it ideal for early personal computers.

DOS today

Eventually, Microsoft found that DOS limitations prevented it from developing an operating system that could compete with Apple’s Unix-based systems. So, the company abandoned DOS starting with Windows NT, Windows 2000, and Windows XP.

Still, that doesn’t mean that DOS has completely disappeared. If you open the Command Prompt application on a Windows machine, you’ll see a command line that looks similar to the old DOS prompts. This isn’t true DOS, but rather a virtual machine environment designed to emulate DOS.

Like with terminal on Macs, developers learn how to use the command line in Windows to work with hard-to-access files within their computers or perform automated tasks that are easier to program with text-based instructions.

Learn how to control your computer without a mouse

Now that you know all about DOS, what’s next? If you’re not sure where to start, we recommend getting familiar with using the command line and learning the basics of Bash scripting.

And, if you’re not sure what else you should learn as a new developer, we’ve got you covered. Our Career Paths will keep you focused on learning all the skills you need to succeed in your new development career.

Bash/Shell Courses & Tutorials | Codecademy

We use a mouse or finger to click icons and access files, programs, and folders on our devices. But this is just one way for us to communicate with computers. The command line and the shell make up a quick, powerful, text-based interface developers use to more effectively and efficiently communicate…

If you’re starting a career as a Front-End Developer, Full-Stack Developer, or Computer Scientist, then you’ve probably started learning Java. Maybe you’ve started with an online course, which is a great way to build a solid programming foundation. Once you’re familiar with the basics, try putting your Java skills to the test with some practical exercises to build on your knowledge.

One of the best features of Java is its flexibility. You may find that there are multiple ways to solve the same challenge. In fact, if you’re learning Java with a friend, try these challenges together and learn from each other by comparing your results.

If you get stuck, try thinking through the problem using pseudocode or a general description of the programming steps you’d use to solve the problem. Pseudocode is helpful because it lets you work through programming challenges without having to worry about the specific syntax of a programming language (you can worry about that later).

Below are 10 Java code challenges for beginners. The first five challenges are with strings, while the last five challenges involve numerical inputs. Let’s get started!

10 Java code challenges to practice your new skills

1. Word reversal

For this challenge, the input is a string of words, and the output should be the words in reverse but with the letters in the original order. For example, the string “Dog bites man” should output as “man bites Dog.”

After you’ve solved this challenge, try adding sentence capitalization and punctuation to your code. So, the string “Codecademy is the best!” should output as “Best the is Codecademy!”

2. Find the word

Starting with an input string of words, find the second-to-last word of the string. For example, an input of “I love Codecademy” should return “love.”

To make your program more challenging, allow for a second numerical input, n, that results in returning the nth word of a string. So, for the string “I can program in Java” and n = 3, the output should be the third word, “program.”

3. Word search

For a given input string, return a Boolean TRUE if the string starts with a given input word. So, for an input string of “hello world” and input word “hello,” the program should return TRUE.

For a more advanced word searcher, create a program that returns the number of times a word appears in an input string. For example, given an input word “new” and an input string “I’m the new newt,” the program should return a value of 2.

4. Anagrams

Two words are anagrams if they contain the same letters but in a different order. Here are a few examples of anagram pairs:

• “listen” and “silent”
• “binary” and “brainy”
• “Paris” and “pairs”

For a given input of two strings, return a Boolean TRUE if the two strings are anagrams.

As an added challenge, for a given array of strings, return separate lists that group anagrams together. For example, the input {“tar,” “rat,” “art,” “meats,” “steam”}, the output should look something like {[“tar,” “rat,” “art”], [“meats,” “steam”]}.

5. Pangrams

A pangram is a sentence that contains all 26 letters of the English alphabet. One of the most well-known examples of a pangram is, “The quick brown fox jumps over the lazy dog.” Create a pangram checker that returns a Boolean TRUE if an input string is a pangram and FALSE if it isn’t.

For an added pangram challenge, create a perfect pangram checker. A perfect pangram is a sentence that uses each letter of the alphabet only once, such as, “Mr. Jock, TV quiz Ph.D., bags few lynx.”

6. Number reversal

This one is a technical interview favorite. For a given input number, return the number in reverse. So, an input of 3956 should return 6593.

If you’re ready for a bigger challenge, reverse a decimal number. The decimal point should stay in the same place. So, the number 193.56 should output 653.91.

7. Armstrong numbers

An Armstrong number is a whole number that’s equal to the sum of its digits raised to the power of the total number of digits. For example, 153 is an Armstrong number because there are three digits, and 153 = 13 + 53 + 33. The four-digit number 8208 is also an Armstrong number, as 8208 = 84 + 24 + 04 + 84.

Create an Armstrong number checker that returns a Boolean TRUE if the input number is an Armstrong number. Hint: to extract each digit from a given number, try using the remainder/modulo operator.

If you’re looking for something a little more challenging, create an Armstrong number calculator that returns all Armstrong numbers between 0 and the input number.

8. Product maximizer

For a given input array of numbers, find the two that result in the largest product. The output should include the two numbers in the array along with their product.

As an extra challenge, use an input of two arrays of numbers and find two numbers — one from each input array — that results in the largest product.

9. Prime number checker

A prime number is any whole number greater than 1 whose only factors are 1 and itself. For example, 7 is a prime number because it’s only divisible by 1 and 7.

Create a function that returns TRUE if an input number is prime. The first few prime numbers are 2, 3, 5, 7, 11, 13, 17, and 19.

For a slightly harder challenge, create a prime number calculator that outputs all prime numbers between 2 and the input number.

10. Prime factorization

The prime factors of a number are all of the integers below that number that are divisible into the number as well as 1. For example, the prime factors of 12 are 1,2,3,4,6, and 12.

Create a prime factorization calculator that returns the prime factors of any number between 2 and 100. If you’re looking for a more advanced version of this challenge, use exercise 9 to create a prime factorization calculator for any number. Hint: think about using square roots to cut your work in half.

Advancing your career with Java

Along with being a fun, low-stress way to test your knowledge of a programming language, code challenges play an important role in helping you prepare for the interview process. If you’re pursuing a career where knowledge of Java is expected, then you’ll be asked to complete a Java-based coding test, as well as other questions related to Java. And, the best way to prepare for that test is to practice code challenges like these.  

To find more opportunities to practice, take a look at our other Java courses, including our popular Java for Programmers course.

Java Courses & Tutorials | Codecademy

Java is one of the most popular programming languages out there. Released in 1995 and still widely used today, Java has many applications, including software development, mobile applications, and large systems development. Knowing Java opens a lot of possibilities for you as a developer.