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.

Behavioural objectives

1. Define an operating system.
2. State what an operating system does between programs and hardware.
3. Name and describe the types of operating system.
4. Distinguish between preemptive and cooperative multi-tasking.
5. Give examples of operating systems.

What does an operating system do?

An operating system controls the hardware and software of a computer and lets users and programs share them.

• System software: the operating system is a component of the system software in a computer system.
• Support for applications: application programs usually require an operating system to function.
• Resource management: it manages the processor, memory, storage, input and output devices.
• Common services: it provides services that many programs need, so each program does not have to supply them.
• Task scheduling: time-sharing operating systems schedule tasks for efficient use of the system.
• Accounting: some include accounting software for cost allocation of processor time, mass storage, printing and other resources.

How does an operating system link programs and hardware?

For hardware functions such as input and output and memory allocation, the operating system acts as an intermediary between programs and the computer hardware.

• Direct execution: application code is usually executed directly by the hardware.
• System calls: the code frequently makes system calls to an OS function to ask for a service.
• Interrupts: the code may also be interrupted by the operating system.
• Input and output: the OS handles requests to read from the keyboard or write to the screen or printer.
• Memory allocation: the OS decides which part of memory each program may use.

Where are operating systems found?

Operating systems are found on many devices that contain a computer, from cellular phones and video game consoles to web servers and supercomputers.

• Microsoft Windows: widely used on personal computers and laptops in Nigerian schools and offices.
• Apple OS X (now macOS): the operating system of Apple computers.
• Linux and its variants: a Unix-like operating system used on servers and personal computers.
• Android and iOS: operating systems for mobile phones and tablets.

What are the types of operating system?

This lesson covers seven types of operating system: single-tasking and multi-tasking, single-user and multi-user, distributed, templated, embedded, real-time and library.

What are single-tasking and multi-tasking operating systems?

A single-tasking system runs one program at a time, while a multi-tasking system runs more than one program concurrently.

• Single-tasking: only one program can run at a time.
• Multi-tasking: more than one program runs concurrently.
• Time-sharing: the available processor time is divided between multiple processes.
• Time-slices: a task scheduling subsystem of the operating system interrupts each process repeatedly in short slices.

Multi-tasking can be preemptive or cooperative.

What is preemptive multi-tasking?

Preemptive multi-tasking is a method in which the operating system slices the CPU time and dedicates a slot to each program.

What is cooperative multi-tasking?

Cooperative multi-tasking is a method in which each process is relied on to provide time to the other processes in a defined manner.

What is the difference between preemptive and cooperative multi-tasking?

What are single-user and multi-user operating systems?

A single-user operating system serves one user at a time, while a multi-user operating system lets several users use the system at the same time.

• Single-user: has no facilities to distinguish users, but may allow multiple programs to run in tandem.
• Multi-user: extends multi-tasking with facilities that identify processes and resources, such as disk space, belonging to multiple users.
• Shared access: a multi-user system permits multiple users to interact with the system at the same time.
• Time-sharing: it schedules tasks for efficient use of the system.
• Accounting: it may include software for cost allocation of processor time, mass storage, printing and other resources to multiple users.

What is a distributed operating system?

A distributed operating system manages a group of distinct computers and makes them appear to be a single computer.

• Origin: networked computers that could be linked and communicate with each other gave rise to distributed computing.
• Computation: distributed computations are carried out on more than one machine.
• Distributed system: computers in a group that work in cooperation form a distributed system.

What is a templated operating system?

Templating is the creation of a single virtual machine image as a guest operating system, which is then saved as a template for multiple running virtual machines.

• Context: it is used in operating system, distributed and cloud computing.
• Use: the technique is used in both virtualization and cloud computing management.
• Where common: it is common in large server warehouses.

What is an embedded operating system?

An embedded operating system is one designed to be used in embedded computer systems.

• Small machines: it is designed to operate on small machines such as PDAs.
• Limited resources: it can operate with a limited number of resources.
• Design: it is very compact and extremely efficient by design.
• Examples: Windows CE and Minix 3.

What is a real-time operating system?

A real-time operating system guarantees to process events or data within a certain short amount of time.

• Tasking: it may be single-tasking or multi-tasking.
• Scheduling: when multi-tasking, it uses specialised scheduling algorithms so that a deterministic nature of behaviour is achieved.
• Event-driven system: switches between tasks based on their priorities or external events.
• Time-sharing system: switches tasks based on clock interrupts.

What is a library operating system?

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

• Composition: the libraries are composed of the application and configuration code used to construct unikernels.
• Unikernels: specialised, single-address space, machine images.
• Deployment: unikernels 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.