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Operating Systems Part 1: Computer Science 3A (CSC3002F)

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These are notes that summarise and combine all the provided lecture slides as well as the additional textbook reading content with important diagrams and visual aids. The OS1 is the 3rd part of the syllabus to be covered and has all the important concepts, algorithms and application examples that y...

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  • May 2, 2023
  • 98
  • 2022/2023
  • Class notes
  • Professor geoff nitschke
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Lecture 1

Readings:
Chapters 1 & 2 in textbook

Considerations when choosing an OS:

1. Resource consumption

2. Security

3. Smart devices need specific OSes




Introduction
What is an OS?


⚡ 1. Textbook def: An OS is software that manages a computer’s hardware. It also
provides a basis for application programs and acts as an intermediary between the
computer user and the computer hardware.
2. A program that lets you run other programs and provides controlled access to
resources. When you start your device, it runs the first program, which is the OS.
3. General piece of software with common functionalities that support many
applications.
4. Operates directly with system hardware.
5. A virtual machine
6. A resource allocator and a control program
7. It is not useful on its own. It provides an ENVIRONMENT within which other
programs can do useful work.




What do they do?
A computer system is made up of:

1. Hardware: Provides basic computing resources for the system: CPU, memory, IO devices
(keyboard, mouse)



Lecture 1 1

, 2. The OS: Controls HW

3. Application Programs: word processors, compilers, web browsers

4. The User




It is a program. Some types:

UNIX OS

Microsoft Windows

Mac OS

Mobile

Can also get custom OSes:

IE, Nintendo switch will make its own custom OS for its products

The kernel is the most NB part.

Translates language into machine level code.

The OS is an illusion: makes it seem like there is CPU and memory etc. The OS initialises
system problems but in itself does nothing. It’s an illusion.

OS as an illusionist:

Clever resource management to overcome hardware limitations

OS as a government:

Protects users from one another

Allocates resources efficiently and fairly




Lecture 1 2

, Provides an environment within which other programs can do useful things.

OS: System View
OS is a resource allocator:

Manages all resources

Handles conflicting requests for efficient and fair resource use

OS is a control program:

Controls execution of programs to ensure the programs run, prevent errors and
improper use of the computer.



Moore’s Law and OSes
Stated that the number of transistors that could be placed on an integrated circuit would
double every 18 months. Therefore computers gained more functionality and shrunk in
size, allowing for a vast variety of OSes to be created.



Abstraction
→ It is simply an abstraction.

Convenience: Hides tedious things

Shows efficiency and control

Allocates resources

Allows parallel applications

Protects information

Interface: Between users and computer (hardware)




Lecture 1 3

, Applications think they have their own dedicated CPU but they don’t. It’s an illusion. Allows programs to run
concurrently. Applications has no idea who else is on the system.




Why have Abstraction?


Why?:

1. Reduce functional complexity

2. Provide single abstraction over multiple devices

3. Resource sharing

a. Efficiency

b. Fairness

c. Security



Examples of Abstractions
A. User Abstraction:




Lecture 1 4

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