The Operating System

We all use one. If asked, "What is an operating system?" however, what would you say? Perhaps, "It's what runs all my apps." Or, "It's the foundation of my computer's software." These are more or less true, but do not really fully explain what an operating system is or what it does.

The Operating System

The Foundation of a Multi-Program Computer

The very first computers did not have operating systems (OS). They would just run one program at a time; when these programs were running, they were the only thing that the machine was doing.

Eventually, computers became able to keep more than one program in storage at one time. The operating system was developed as a way to handle various programs. However, each program was independent from anything else.

Later, computers were developed which had data and services based on the machine, which were used by various programs. More and more, the operating system became the base "program" operated by the user, with other programs being launched "on top of" or "within" the operating system.

The operating system developed what is called the kernel. The kernel is the main controller of software on the computer. When the computer is started, the kernel loads first, and controls everything from then on. The kernel provides the central functions of the operating system. The rest of the operating system is a constellation of software that provides a variety of functions and services.

The kernel's job is to provide a workspace from which programs can run. It controls storage, memory and the CPU; it decides how computer resources are handled. It allows the user to launch programs, and then it controls the programs' access to hardware.

For example, if you open a program, the kernel handles the transfer of the program from storage to memory, and then to the CPU. The program requires access to input from the keyboard and mouse; the kernel makes that connection, allowing the program access to that hardware. When the program needs to output something, such as video or audio, it again asks the kernel for permission, and the kernel controls that.

In short, the kernel has control over the hardware of the computer, giving access to programs when they need it.

A Government for Your Computer

A way to think of the overall operating system for a computer is that it serves as a government, or as a society for that computer. Just like people and businesses depend upon social services, both you and the programs you use depend upon the operating system to provide basic services that are needed.

For example, if you wish to build a house, what do you need?

  • Electricity
  • Water / Sewage
  • Gas
  • Garbage removal
  • Telephone service
  • Roads
  • Police protection
  • Fire protection
  • Military protection
  • Etc. ...

So, what will you do? Will you build your own road to your house? Will you get a generator and create your own electricity? Will you drill for natural gas, or perhaps buy large tanks of gas and keep them in your yard? Will you drill a well to get water, and take care of your own waste? Will you hire private police to protect you? And so on…

Of course, you will not do these things. That's what societies are for: they provide most or all of these basic services. This is important, because if we did not have these services, then it would be very expensive and terribly difficult and time-consuming just to carry out the basic tasks of everyday life.

In the same way, computer programs (also called "software" or "applications") do not have to take care of all the normal tasks that are necessary on a computer.

For example, let's say that I want to create a simple game. For that game, I need these services:

  • Video (to show my game)
  • Audio (to play sounds made in my game)
  • Keyboard (to control the game)
  • Mouse (also to control the game)
  • Fonts (to show text in my game)
  • Networks (to allow playing with other people)
  • Etc. ...

Now, if I had to create software for video and audio and keyboard and mouse and fonts and networking and all the other basic computer functions just for my little video game, I would have to spend years developing even just simple software.

Fortunately, the Operating System does all of that for me. I just have to know how to "call" for each service, and after that I don't have to do very much.


Your computer's kernel understands how to use the basic hardware of the computer, but all sorts of devices are then attached. Each one requires specific knowledge to operate all of its features. Software called a driver (or a "device driver") is installed for the operating system to use, so it can understand the new hardware and use all of its features.

For example, if you add to your computer a blu-ray burner, a gaming mouse, a printer, or a scanner, your operating system may not know how to use it. Often these devices come with software which allows you to install the device drivers necessary. If you do not have the driver for a device, you cannot use it.

After you install a driver, your computer should be able to use the new device smoothly. In addition, you may find new controls available for your device in the control panels, preferences, or even in menus.

A good example of what a driver is can be found in the movie The Matrix. In that movie, if a person wants to learn a new skill, they just get a "training program" for the skill uploaded to their brain. This is similar to how a driver works.

Today, operating systems often include a large number of printer drivers pre-installed, so you can quickly connect to and use almost any printer.

One problem with drivers is that they are usually designed for a specific operating system version. For example, a driver made for a scanner on Windows XP may not work using Windows 7. Upgrading the operating system may require upgrading the driver.

Points to remember:

  • Drivers are needed to run most hardware devices
  • Drivers are installed into an operating system
  • Drivers are designed for specific operating system versions
  • Some drivers may be found in store-bought operating system software, but most need to be installed from a special driver volume included with the hardware, or else downloaded from a manufacturer's site and then installed


Firmware is software stored on a device which helps operate the device. Firmware is kept on a ROM (or programmable ROM) chip inside the device. Most electronic devices have firmware. For example, your TV's remote control has firmware. Your DVD player has firmware. Your refrigerator probably has firmware.

Firmware is used directly by the device itself, in the absence of an OS or other software. Firmware tells the device how to work. For example, your printer can work even when your computer is not connected to it; it uses its firmware to operate independently. That firmware will work together with your computer (often via the device driver) when they are connected and the computer uses the device. Even when the device is always connected to a computer (as with an optical drive), the firmware could perform much faster than the OS using driver software.

Devices used with computers often have firmware on Flash ROM. "ROM" (read-only memory) often cannot be updated, but Flash ROM can be. You may find that your computer's update center alerts you to update the firmware of certain devices, like your WiFi base station, your printer, or your optical drive. Your digital camera might take a firmware upgrade.

Firmware is not updated very frequently. Firmware is considered more "permanent," and is updated only when necessary for issues such as security or performance.

Operating Systems

Major Operating Systems

The two major operating systems are Windows and macOS, with Linux running a distant third. Worldwide, Windows makes up about 88% of Desktop operating systems; macOS has about 10%; Linux has about 1.5%. Amongst developers (people who create software), however, only 52% use Windows, 26% use macOS, and 22% use Linux.

The major operating systems and the hardware they work on are generally referred to as platforms. A "platform" is a foundation upon which software can run. Normally, two major platforms are referred to as Windows and Macintosh. In the past, Macintosh and Windows used completely different hardware systems, making the platforms completely distinct; when Apple switched to using Intel chips (called the x86 family), the platform differences became more a matter of the operating systems themselves, as they now use essentially the same hardware platform.

Linux is a software "platform" in that software must be written specifically for Linux to run on it; however, in regards to "hardware" platforms, Linux can run on many different types of devices, including mobile and handheld. In a hardware sense, Linux is cross-platform.

Cross-platform can mean two things: (1) either software can be directly used on various hardware platforms (like Linux) or hardware/software platforms (for example, web apps can run on most operating systems), or (2) software is written and then versions are created which run specifically for different operating system platforms (for example, Firefox has versions for Windows, macOS, and Linux).

Most software is written specifically for an operating system platform. If this software is later changed so it can be run on a different operating system, it is called a port; this is also a verb, as in, "The game was later ported to the Mac."

On mobile devices (tablets, smartphones, etc.), Android (developed by Google based on Linux) dominates, holding 65% of the market; Apple's iOS has 24%, and Windows trails with less than 2%.



In the 1970's, the UNIX operating system was developed and became extremely popular. It was a modular operating system, meaning that it was not just one program, but a collection of many programs. It has remained popular ever since, and has been the model or direct basis for many other operating systems, including macOS and Linux.

Apple's ProDOS

When personal computers first emerged in the late 70's, they ran command line interfaces, or CLIs, usually referred to as DOS (Disk Operating System). These were text interfaces, with no mouse, no desktop, icons, or windows. Apple used Apple DOS, for example, and later ProDOS. Despite many stories about Apple being a giant in the early market, however, Apple never had more than 15% of the PC market.



Microsoft originally did not make an operating system; it started as a company that developed programming languages and associated software. In 1981, IBM built a computer design which it intended to compete with other makers like Apple; they asked Microsoft to develop an operating system for it.

Not having an OS, Microsoft went and bought one. They reportedly paid $50,000 or $75,000 (stories about this differ) to the Seattle Computer Products company for an operating system that was developed under the name QDOS, or "Quick and Dirty Operating System." Microsoft refined the OS to work on the IBM PC, and renamed the product MS-DOS (Microsoft Disk Operating System).

Microsoft famously made the best decision in its history when it decided to license the new OS to computer makers, instead of selling it to IBM directly. This eventually led to Microsoft's dominance in the computer industry.

The first Mac OS

Meanwhile, Steve Jobs at Apple heard about a new operating system being developed at Xerox's Palo Alto Research Center (PARC). The operating system was a GUI (Graphical User Interface), which used a mouse and had a desktop, windows, and many other elements we are now all familiar with. This OS was based upon principles developed by Douglas Engelbart, who created many of the concepts used in GUIs. Xerox was not really interested in this project, so they happily allowed Jobs and Apple to study and adopt the design in exchange for the chance to buy Apple stock at a very low price.

The first Windows GUI

Jobs then led a team of engineers and programmers in creating a new line of GUI-based Apple computers. The project split into two parts; one released the Lisa in 1983, but it flopped because it was far too expensive. Jobs himself led the team that created the Macintosh, released in 1984.

The Macintosh used an entirely different operating system than Apple's earlier successful computers; it was called Mac OS. Mac OS eventually went through 9 major versions (and dozens of smaller updates) before it eventually was replaced in the early 2000's.

Steve Job's NeXTSTEP OS

Meanwhile, Microsoft was aware of the new GUI style that was destined to dominate computers, but unlike Apple, Microsoft did not throw away it's CLI-based MS-DOS; instead, it built a GUI on top of the existing DOS software. The first Microsoft Windows version was born.

Because Microsoft developed software for Apple, and was required not to copy Apple's designs too closely, the GUI was very limited, and was not very popular.

In the mid-1980's, things started shaking up. Steve Jobs was fired by Apple, and started a new company called NeXT, with its NeXTSTEP OS which was built using Unix. This was developed over the second half of the 1980's.

IBM's OS/2 Challenge to Microsoft

Microsoft, on the other hand, was having difficulty with its partnership with IBM. The two companies agreed to develop a new operating system which was fully based on the GUI (instead of Microsoft's incomplete solution of creating a GUI-like OS on top of DOS). This new operating system was to be called OS/2. Unfortunately (for IBM), this partnership broke up. IBM developed OS/2, but it was never very popular.

Windows 3.1


In 1990, Microsoft released Windows 3, and then Windows 3.1 in 1992; this version finally became widely popular, though it was still based on MS-DOS. Together with extremely cheap PCs being built on the original IBM pattern, this combination took control of about 90% of the computer market by 1995.

Windows 95

In the meantime, a young student in Helsinki, Finland named Linus Torvalds created his own operating system kernel. He called it "Freax," but instead, the name Linux, based upon his own name, became popular instead. Linux was offered for free, and could be modified and released by anyone. While it began to spread more widely in the mid-1990's, it never gained widespread popularity.

the Mac OS develops; v. 7.5

While Apple continued to develop its Mac OS line, Microsoft was working on its own GUI-based OS. Called Windows NT, it struggled along during the early 1990's, and was sold primarily to business users. Microsoft wanted to merge NT with its consumer OS versions in 1995, but failed.

Instead, Microsoft released Windows 4—also known as Windows 95—in the last weeks of 1995. The new OS had a look that Microsoft would stay with until 2012.

In 1998, still based on MS-DOS from 1981, Windows 98 was offered by Microsoft with a big change: the OS interface became tied in with the company's Internet Explorer browser. This was the first time we began to see history buttons outside of the browser, allowing windows to work like web pages.

Apple's market share, which had shrunk to 5% in 1995, eventually fell to just 2%. The company was widely seen as being in trouble. In 1997, Apple hired Steve Jobs back, buying his (not-so-successful) NeXT company, and appointing Jobs as CEO. Jobs began working on a plan to take his NeXTSTEP OS and use it to replace the Mac OS.

An Early Linux GUI

Linux continued to be popular with a small core of users, gaining more and more interest, especially with those who disliked Windows and Mac OS both—but never gained large numbers of users. For a long time, the OS was viewed as highly technical and difficult to use—an operating system only for experts and hobbyists. Linux was released by many vendors, and quickly acquired GUI shells. Most Linux GUIs strongly resembled the Windows and Mac GUIs of their time.


After a disastrous release of the much-hated Windows ME in 2000, Windows finally abandoned MS-DOS in 2001 when it released Windows XP, which finally introduced NT technology into Microsoft's consumer OS line. Windows XP would continue as Microsoft's most popular OS version until 2009.

The First Mac OS X

Steve Jobs, meanwhile, successfully created his new Unix-based version of the Mac OS, which was called Mac OS X (either "Oh-Ess-Ten" or "Oh-Ess-Ex"). Pre-released in 2000, the first full official release was in early 2001.

With each major version named after a large cat (Cheetah, Puma, Jaguar, Panther, etc.), they were also referred to as "point" releases—10.1, 10.2, 10.3, and so forth. Apple released a new version of its OS every one to two years. Apple is currently releasing macOS version 10.12 (Apple dropped the "X" in the name earlier in 2016, due to its diverse appeal with many operating systems).

The First iPhone's iOS

This was in marked contrast to Microsoft, which was having trouble coming up with a new version of Windows. XP was quite stable and popular, and Microsoft couldn't get a new OS to work the way they wanted. Between 2001 and 2007, Apple released 6 versions of its operating system, while Microsoft struggled to release one new version.

Unfortunately, that new version was Vista. Vista was a disaster, suffering many problems and leaving some users angry and unable to fully use their computers.

Apple, in contrast, was seeing huge success; after the gigantic success they enjoyed with the iPod line of products, they scored another home run with the iPhone, which used a new mobile OS named iOS. This was later added to with Apple's tvOS and the newer watchOS.

The iPod and iPhone both generated something called the Halo effect, in which many people who were pleased with their iPods and iPhones began to use other Apple products as well. Apple's market share steadily grew from 2% at the start of the decade to as much as 8% worldwide in 2016 (15% in the United States).

Windows 8's "Metro" GUI

Windows finally came out with a stable release in 2009 called Windows 7 (no explanation why the number "7" was used). While stable and newly popular, Windows 7 was criticized for having too many versions, with the cheapest versions lacking significant features.

In 2012, Microsoft again suffered disaster with Windows 8. When Apple began to challenge Microsoft's market share with it's cute, trendy "Mac vs. PC" ads, Microsoft responded by pointing out that a great advantage of Windows was that most people were comfortable with the interface. However, Windows 8 completely redesigned the interface, without any kind of guide to train users in how to use it, leading to massive confusion and discontent. Gone was the Desktop Windows had used since 1995, as well as the very popular Start Menu.

Microsoft pulled back a little in version 8.1, and pulled back much further in 2015 when they released Windows 10, re-introducing the Start Menu.

Special Features

An operating system does not just provide data services and hardware links to applications; it also has a number of special features that it makes available to the user. These features are usually a strong selling point for the entire platform.

Windows Features

The Taskbar and Start menu: Since 1995, these have been a standard in Windows, and perhaps its most liked features. The Taskbar is home to three major parts: the Start Menu; active windows, essentially icons which indicate open programs; and the System Tray.

The Start Menu itself has many parts; it includes a list of programs one can open; the power options, including restart, shut down and log off; links to important locations on the computer; access to the control panel; and, more recently, a search bar. In Windows 8, the Start Menu was discarded in favor of a panel-based, more touchscreen/tablet style of interface, called Metro. So many people complained that Microsoft brought the Start Menu back in Windows 8.1, and later merged the Start Menu and the Metro interface in the new Start Menu in Windows 10.

Next to the Start Menu in the Taskbar, there used to be button representing open windows; since 2007, this changed to application icons. Called Pinned Applications, they act similarly to the Start Menu application list (also now called "pinned" to the Start Menu), providing shortcuts to open the user's favored programs. When a program is open, a color bar appears under the icon. To see all open windows in the application, hover the cursor over the icon, and Aero Peek will show thumbnail images of the windows, from which you can choose. Clicking on the program icons will open them, but right-clicking them will show a Jump List, with pinned documents, recently opened documents, tasks that the program can do, and options such as close window.

Finally, there is the System Tray, home to the date and time, but also to various icons for utilities and features connected to operating system functions and applications in use. Sound, network, and battery status and controls are available, as well as controls to eject volumes. In addition, any application or process that may allow or need your attention may have an icon here, such as security, messaging, or system utilities.

Aero Snap: a surprisingly useful feature is when you grab a window by the title bar and then move it to the top, left, or right edge of the screen. When the cursor dragging the window hits the edge, the window expands. If you drag the window to the top, it expands to full screen; if you drag it to the sides, then the window resizes to fill that half of the screen. This allows for easy access to full-screen status for one window, or split-screen access to two separate windows.

Aero Shake: A less-known feature allows you to grab a window by the title bar, and then, by shaking it a little, cause all other open windows to minimize all at once. Alternately, all windows can be minimized by either typing the keyboard shortcut Start + D, or by clicking on a small, thin button in the corner of the screen to the right of the System Tray

A New Edge: Internet Explorer has been around since the mid-90's, and was actually based upon Mosaic, a very early browser and antecedent to Netscape Navigator. After IE killed off Navigator in the late 90's, it was the #1 browser. However, because of poor security and speed, and because the browser failed to evolve as newer browsers leaped ahead, IE got a terrible (but many say well-deserved) reputation for being the worst of all browsers. Web designers especially grew to hate the browser, as its refusal to use universal standards created uncountable headaches when designing web pages. After many years of falling behind, Microsoft finally decided to phase out Internet Explorer.

The new browser is called Edge, and is included with IE in Windows 10. It has better application of universal standards, and a good set of new features. However, Edge is still under construction, and many features are still incomplete or missing.

Cortana is a digital personal assistant (similar to Siri), able to answer a number of questions, lead you to utilities or controls you may need, or lead you to an Internet search. You can type the question, or click on the microphone button and speak the query.

Action Center: Activated by a touchscreen/trackswipe from the right, or by clicking on the Action Center icon in the System Tray, this pane can present all manner of notifications from various apps and operating system functions. Calendar, Mail, Social Media, Cloud Storage, Application notifications, and much more can be presented here in one central area.

Task View (formerly Flip 3D): in previous Windows versions, one could browse open windows with the ALT + TAB keyboard shortcut. In Windows 7, this evolved into Flip 3D, a cool way to access windows as they flew by you in 3D space—a flashy but essentially needless graphics display. In Windows 10, the feature is called Task View, and is activated by the START + TAB shortcut, or by clicking on the Task View icon just to the right of Cortana's search window. Additionally, if you have several windows open, and use Aero Snap to expand a window to half-scree size, the other open windows assemble in Task View on the opposite side—a feature called Snap Assist—in case you want to grab one of them and put it on the other side.

Macintosh Features

Below is a list of some of the major features of Mac OS, which has offered free upgrades since 2013:

Languages: the Mac OS can switch languages for both input and at the operating system level. Windows comes in different versions, and only the more expensive ones have the ability to change the base language of the operating system. Mac OS, however, has just one basic version, and it has allowed users to change the base language since the first version of OS X. Applications written for the Mac OS have localizations which allow the app to change to various languages; as a result, if you change your Mac's base language, most of the apps you have will automatically also switch to that language.

Dictionary: the Mac OS includes a bundle of dictionaries, including the Oxford Dictionary and Thesaurus, as well as various cross-language dictionaries. This app is tied into the operating system so that you can, in various apps, triple-tap on a word and a dictionary window will come up with the definition of that word.

Native PDF support: Since its earliest OS X version, the Mac OS has had PDF support at the system level; any time you want to save any document from any app as a PDF, just open a Print dialog box and select the PDF menu from the lower right; anything you can print, you can save as a PDF.

Mission Control (formerly called Exposé): Allows you to view all open windows in an app you are using; alternately, you can view all open windows in all applications. Once Mission Control is activated, you will see all the windows spread out side by side; click on one of them will switch to that window and/or application. Mission Control also allows you to see the Desktop, sweeping all visible windows out of the way. Icons or selected text can be dragged between a window and another window or the Desktop.

Quick Look: allows a user to see the contents of a file by pressing the space bar while the icon is selected; a window will appear showing the a preview of the file.

Time Machine: Apple's backup service, allowing an external hard drive to hold backups of the entire computer, adding to the backups over time, and allowing users to either browse through past files, or else re-install past computer states onto a new or newly-wiped Mac.

Boot Camp: Allows a use to install Windows (but not Linux) on a Mac as a dual boot. A dual boot is when one computer hosts two separate operating systems. Only one can be used at one time; when you want to switch, you have to shut one operating system down, restart, and then boot up another one.

Notification Center: a feature which allows various programs and services to notify the user of messages, alerts, and other events in one location.

Siri: a voice-controlled personal assistant, originally offered only on mobile platforms.

Cross-Device Integration: Recent versions of the OS allow for greater communication between various Apple devices. For example, Handoff allows a user to take Internet browsing, email authoring and reading, text messaging, and other work from a mobile device and continue working on the document on a desktop or laptop, or vice-versa. Airplay allows music or video playing on one device to be transferred to a different device. Other features include the ability to answer or make telephone calls from a networked Mac computer, or from another device like an iPad.

Bundled Apps: Apple offers a large number of free applications made by the company on any Mac computer; most of these apps offer suite-like connectivity between them. The apps include App Store, Automator (for advanced users to create scripts which add functionality to the computer), Contacts, Dashboard (which launches mini-applications, usually small utilities), Dictionary, DVD Player, Font Book, Game Center, Garage Band (a music authoring app), iBooks (an ebook reader), iBooks Author (an ebook creator), Image Capture (downloads images from devices, or captures scans from connected printers or scanners), iTunes, Keynote (an app similar to PowerPoint), Launchpad, Mail, Maps, Messages, Notes, Numbers (an app similar to Excel), Pages (similar to Word), Photos, Preview (opens and edits PDFs and Images), QuickTime media player, Reminders, Safari (Apple's browser), and various utilities, such as Disk Utility, Terminal, and Activity Monitor. ,

Terms to Know

kernelthe core of a computer operating system; the kernel opens first, and then the kernel loads and opens the rest of the operating system..
driversoftware which "teaches" the operating system how to use new hardware, or to access special features of the hardware.
firmwaresoftware on a chip inside a computer, peripheral or other device. Firmware acts like a low-level operating system, granting the user direct access to hardware controls. Many home appliances have firmware, as do most computers. Firmware often allows a user to operate a peripheral device without the assistance of a computer.
platforma hardware or software foundation upon which specific apps can run. Most apps are able to run only on one platform; software that can run on multiple platforms is called "cross platform".
portto rewrite the code for a program so it can run on a different platform, or the name for such a version.
command linealso CLI. A text-only interface for a computer.
graphics user interfacealso GUI. A graphical interface, using visual metaphors to make it easier for people to understand and use the computer.
PlatformThe foundation upon which software can run; today, an operating system.
Cross-Platformsoftware that can be used on more than one OS.
Porta translation of software for a new computer platform.
MS-DOSMicrosoft's command line OS for IBM PCs.
Douglas EngelbartTechnology wizard. Invented the GUI and the Mouse.
Mac OSThe GUI Macintosh computer operating system.
Microsoft WindowsMicrosoft's version of the GUI, based on MS-DOS until the 1990's or early 2000s.
UNIXA 1970's command-line OS which has become the basis for many operating systems, including Mac OS X.
LinuxA free OS modeled after UNIX..
Halo EffectIncreased sales of many items made by a company as a result of one product becoming highly popular.

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