Operating System – SS1 Data Processing Lesson Note (Second Term)

An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs. The operating system is a component of the system software in a computer system. Application programs usually require an operating system to function.

Behavioural objectives

By the end of the lesson, students should be able to:

• define an operating system;
• state what an operating system does between programs and hardware;
• name and describe the types of operating system;
• distinguish between preemptive and cooperative multi-tasking;
• give examples of operating systems.

What does an operating system do?

Time-sharing operating systems schedule tasks for efficient use of the system. They may also include accounting software for cost allocation of processor time, mass storage, printing and other resources.

For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware. The application code is usually executed directly by the hardware and frequently makes system calls to an OS function or is interrupted by it.

Operating systems are found on many devices that contain a computer, from cellular phones and video game consoles to web servers and supercomputers. Examples of modern operating systems include Apple OS X, Linux and its variants, and Microsoft Windows.

What are the types of operating system?

Single-tasking and multi-tasking

A single-tasking system can only run one program at a time. A multi-tasking operating system allows more than one program to run concurrently. This is achieved by time-sharing, which divides the available processor time between multiple processes. Each process is interrupted repeatedly in time-slices by a task scheduling subsystem of the operating system.

Multi-tasking can be preemptive or cooperative.

Single-user and multi-user

Single-user operating systems have no facilities to distinguish users, but may allow multiple programs to run in tandem.

A multi-user operating system extends the basic concept of multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users. The system permits multiple users to interact with the system at the same time.

Time-sharing operating systems schedule tasks for efficient use of the system. They may also include accounting software for cost allocation of processor time, mass storage, printing and other resources to multiple users.

Distributed

A distributed operating system manages a group of distinct computers and makes them appear to be a single computer. The development of networked computers that could be linked and communicate with each other gave rise to distributed computing.

Distributed computations are carried out on more than one machine. When computers in a group work in cooperation, they form a distributed system.

Templated

In an OS, distributed and cloud computing context, templating refers to creating a single virtual machine image as a guest operating system, and then saving it as a tool for multiple running virtual machines. The technique is used in both virtualization and cloud computing management, and is common in large server warehouses.

Embedded

Embedded operating systems are designed to be used in embedded computer systems. They are designed to operate on small machines like PDAs with less autonomy.

They can operate with a limited number of resources. They are very compact and extremely efficient by design. Windows CE and Minix 3 are some examples of embedded operating systems.

Real-time

A real-time operating system is an operating system that guarantees to process events or data within a certain short amount of time. A real-time operating system may be single-tasking or multi-tasking. When it is multi-tasking, it uses specialised scheduling algorithms so that a deterministic nature of behaviour is achieved.

An event-driven system switches between tasks based on their priorities or external events, while time-sharing operating systems switch tasks based on clock interrupts.

Library

A library operating system is one in which the services that a typical operating system provides, such as networking, are provided in the form of libraries.

These libraries are composed of the application and configuration code to construct unikernels, which are specialised, single-address space, machine images that can be deployed to the cloud or embedded environments.

Evaluation

1. Define an operating system.
2. Explain the difference between a single-tasking and a multi-tasking operating system.
3. State one difference between preemptive and cooperative multi-tasking.
4. What is a distributed operating system?
5. Name two examples of embedded operating systems.

Assignment

1. List the seven types of operating system covered in this lesson and write one sentence on each.
2. Explain how a multi-user operating system differs from a single-user operating system.