What Is an Operating System?

A woman works on a laptop thanks to an operating system

With computing devices becoming so ingrained in daily life, most people have some awareness of operating systems. For many, the knowledge might be surface level – people might recognize Windows or Android as a distinguishing feature of devices but not really understand what that means. For IT professionals, the operating system is a critical element when it comes to managing and supporting computer programs. Whether it is the hardware devices used by employees or the other components across the IT architecture, understanding the basic concepts of operating systems is part of the foundational knowledge needed for success in an IT career.

Operating System Defined

To define the term operating system, let’s think in terms of stacks – one of the most common models used to describe computer systems. From network operations to software applications to emerging technology, solutions usually have multiple pieces that build on each other. Operating systems are no different.

The operating system, or OS, is best thought of as the middle layer of a basic computing stack, connecting the computer hardware to applications.


A diagram illustrating how operating systems connect applications to hardware.

The hardware is the foundation of any computing device – the physical pieces such as processors, memory or input/output ports. Direct access and control of this hardware is not user friendly because it only understands certain commands, and these commands are directly tied to the function of the hardware in a way that many people do not understand.

This is where an operating system comes in. The OS acts as a translation layer, creating user-friendly options, like a graphical user interface (GUI) with point-and-click capability, that are mapped to the hardware command language.

Of course, having access to the hardware is still not very useful for the average user. That access alone does not allow people to write documents, view pictures or surf the internet. For those actions, system software applications are needed. The most common way that an OS is used is as a platform for software developers, who use the translation capabilities to build application programs for end users

What Is an Operating System Kernel?

The stack model can also be applied to the operating system itself. The primary piece that performs translation for the hardware is known as the kernel. Given the costs involved with developing both hardware and software, there are clearly constraints around building new kernels, and the dynamics between hardware components and OS kernels have defined much of the current IT industry. This will be explored more in the section on different operating systems.

A diagram illustrating how the operating system (libraries, API, UI) is built on top of the kernel to direct the hardware.

The features that truly make an OS usable are built on top of the kernel:

  • Software libraries that are unique to a given OS
  • The application programming interface (API) that allows developers to build applications
  • The user interface (UI) that makes a device accessible to everyone, regardless of technical expertise
  • What Is Firmware?

    Firmware is a specialized example of an operating system. The most popular operating systems are designed to be flexible. They can be used on many different devices, and they can act as a platform for many types of applications. Firmware is a much more focused device driver. Rather than providing openness, firmware is directly tied to specific hardware and provides a limited set of functions.

    The reason that firmware is used rather than a more open operating system is performance. By focusing specifically on the exact hardware used and by limiting the functionality, developers can improve real-time performance and efficiency, or they can deliver a specific level of performance at a reasonable cost. This is important in situations where performance is critical or the functionality is already limited and cost becomes a major factor. Firmware is found in many single-purpose devices, such as printers and smart devices used in the internet of things.

    Firmware vs. Software

    Technically, the term software is very broad, covering any product written in a programming language that runs on computing hardware. In most cases, people use the term software when referring to applications that help with multitasking, such as spreadsheets, photo editing or video games.

    However, operating systems and firmware are both examples of software as well. Since they usually come pre-installed and are tied so tightly to the basic operation of a device, they are more transparent for most users. However, operating systems are a type of software, and firmware is a type of operating system.

    A venn diagram showing that firmware is an operating system and an operating system is software, therefore firmware is software.

    What Does an Operating System Do?

    An operating system has three primary functions:

    1. Managing the hardware
    2. Enabling the operating of software applications
    3. Making the device usable

    First, the OS manages the hardware on the device. This may include a central processing unit (CPU), a graphics processing unit (GPU), memory (including RAM and hard drives) and input/output (including keyboard, monitor, USB ports, etc.). All of these components perform different functions, and they usually come from a variety of suppliers. Tying it all together and making it work cohesively is the first job of the OS.

    Second, an OS provides access for other developers to build software. For general purpose systems – such as personal computers and mobile devices – people want to perform a wide variety of tasks. Software developers can utilize the API provided by an operating system to build out the functionality of their program. Of course, different kernels use different APIs, so developers who want their software on multiple platforms have to build multiple versions.

    Finally, an OS makes the device usable. Some operating systems only have a command-line interface, and users must have specific expertise to understand which commands to use. Other operating systems have a GUI, making the operation of the device much more accessible. Over the past decade, the types of UI have evolved to include touchscreens, gestures and voice commands.

    What Types of Operating Systems Are There?

    As the computing landscape has changed, so has the variety in operating systems. The operating systems on the market today range from the well-known to the misunderstood to the obscure.

    Common Desktop Operating Systems

    Windows: Microsoft’s desktop OS is possibly the most important piece of software in tech history. In the 1980s, Microsoft developed a partnership with Intel, and the combination of the Windows operating system with Intel processors (known as the Wintel platform) took the world by storm.

    Microsoft Windows became the OS used by a majority of people as the PC reached mass adoption – in January 2010, Windows was on 92% of all computing devices worldwide. Today, Windows is still a critical fixture, especially in business, where both Windows laptops and servers are well entrenched.

    macOS: Historically, Apple’s desktops and laptops have not enjoyed the same market presence as Windows machines, but the original MacIntosh operating system introduced several GUI concepts that were later featured in Windows. As Apple became dominant in the mobile space, its Mac platform grew as well, with the OS evolving into OS X and now the current iteration as macOS.

    As of April 2020, macOS has 19% market share in the desktop/laptop space, and it has become more prevalent in business, with many firms offering dual support for both Windows and Mac machines.

    Linux: Linux is … complicated. The history of Linux starts with the UNIX OS, released in 1971 by AT&T’s Bell Labs and made popular through the 1970s thanks to portability to different computing platforms and the antitrust requirement for AT&T to freely provide licenses when asked. When Bell Labs made UNIX proprietary after being divested from AT&T, the GNU Project was started to create free UNIX-like software.

    In 1991, the Linux kernel was developed and incorporated into the GNU project, leading to an explosion of operating systems based on the Linux kernel. While the term Linux is often used as a name for an OS, there are technically many versions of the Linux operating system (known as distributions). These distributions, such as Ubuntu or Red Hat Enterprise Linux, are found in a wide variety of computing devices, including IBM.

    Chrome: Google’s Chrome OS, used primarily in Chromebook laptops, is one of the operating systems based on the Linux kernel. It uses the Chrome browser as the primary user interface, limiting the user’s ability to access applications outside of the browser. This transfers most of the computing complexity to the internet, driving down the cost of the devices. Thanks to the low cost and the high degree of control, this Chromebook operating system has become popular in the education vertical.

    Common Mobile Operating Systems

    A pie chart showing the market share of major operating systems: Android, Windows, iOS and macOS.

    Android: Also based on the Linux kernel, Android is an OS for smartphones and

    Because Android is free and open source, it has been used by many device manufacturers and has become the most popular OS in the world. As of April 2020, Android has 39% market share, compared to 33% for Windows, 17% for iOS and 8% for macOS(Statcounter). 
    tablets. The Android operating system was originally developed by Google and is now developed and maintained by the Open Handset Alliance, which is sponsored by Google.


    iOS: In contrast to Android, Apple’s iOS is proprietary and only found on its own devices. In 2019, Apple announced that iPads would run on a variant of iOS known as iPadOS, but both iPhones and iPads are still generally considered iOS devices.

    Although Android has greater market share, iOS devices dominate the high end of the mobile market, making iOS more attractive to developers and giving iOS the appearance of relatively even standing with Android.

    Operating Systems Used in Internet of Things (IoT) Devices

    Most IoT devices have firmware rather than a full OS, since the device has limited functionality and greater constraints around performance, power consumption and cost. This firmware is often either proprietary or based on the Linux kernel.

    In the cases where a device might have a more robust operating system, the OS is somewhat transparent. For example, Amazon’s Echo devices use Fire OS, Amazon’s proprietary OS based on the Linux kernel. However, most people don’t recognize Fire OS as part of the device, typically identifying more with the Alexa UI.

    For IT professionals, understanding the basics behind operating systems and the different ways that they might appear on devices is a key part of providing support. As part of the standard technology stack, operating systems are the bridge between the user that has a job to do and the hardware resources that can get the job done.

    IT support professionals, such as help desk technicians, interact with operating systems daily. CompTIA A+ covers the skills needed to install, manage and troubleshoot operating systems. Download the exam objectives for free to see the skills you need to work in IT support.

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