How Operating Systems Work

Types of Operating Systems

privacy notice appears on an iPhone 12
This privacy notice appears on an iPhone 12 under the iOS 14.5.1 operating system. IOS is the system used by Apple products. Christoph Dernbach/picture alliance via Getty Images

Within the broad family of operating systems, there are several types, categorized based on the types of computers they control and the sort of applications they support. The categories are:

  • Real-time operating system (RTOS) - Real-time operating systems are used to control machinery, scientific instruments and industrial systems. An RTOS typically has very little user-interface capability, and no end-user utilities since the system will be a "sealed box" when delivered for use. It is important that an RTOS is managing the resources of the computer so that a particular operation executes in precisely the same amount of time every time it occurs. In a complex machine, having a part move more quickly just because system resources are available may be just as catastrophic as having it not move at all because the system is busy.
  • Single-user, single task - As the name implies, this operating system is designed to manage the computer so that one user can effectively do one thing at a time. MS-DOS is a good example of a single-user, single-task operating system.
  • Single-user, multitasking - This is the type of operating system most people use on their desktop and laptop computers today. Microsoft's Windows and Apple's macOS platforms are both examples of operating systems that lets a single user have several applications in operation at the same time. For example, it's entirely possible for a Windows user to be writing a note in a word processor while downloading a file from the internet and printing the text of an email message.
  • Multiuser - A multiuser operating system allows many different users to take advantage of a computer's resources simultaneously. The operating system must make sure that the requirements of the various users are balanced, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn't affect the entire community of users. Unix, VMS and mainframe operating systems, such as MVS, are examples of multiuser operating systems.
  • Distributed - These operating systems manage multiple computers at the same time. Rather than using a single powerful computer to work on large problems, distributed OSes break it down into pieces among many smaller computers. You may find these systems in giant server farms, but hobbyists and educators create their own distributed systems too using inexpensive machines and even repurposed gaming consoles.

It's important to differentiate between multiuser operating systems and single-user operating systems that support networking. If you work in an office where a system administrator controls what software you can or can't have on your work computer, you are using a single-user system that is part of a network. You may print a document on a printer shared with other employees, or have a file server that stores your department's documents.


With the different types of operating systems in mind, it's time to look at the basic functions provided by an operating system.