Part 1 - Operating systems

What is an operating system?

A program that manages a computer's hardware. It also provides a basis for application programs and serves as an intermediary between the user and the hardware.

What does the OS provide?

- Abstraction

- Resource management

What is meant by abstraction when talking about what the OS provides?

That it provides a standard library for resources.

What are resources to an OS?

CPU, memory, disk etc.

What does the OS provide to the CPU in terms of abstraction?

Process and/or thread

What does the OS provide to the memory in terms of abstraction?

Address space

What does the OS provide to the disk in terms of abstraction?

Files

What are some advantages of having the OS provide abstraction?

- It separates interface and underlying hardware implementation

- It allows applications to reuse common facilities

- It makes different devices look the same

What is meant by resource management when talking about what the OS provides?

That the OS manages resources and shares them in a good manner

What are some advantages of having the OS provide resource management?

- Protects applications from one another

- Provides efficient access to resources (cost, time, energy)

- Provides fair access to resources

What are two key concepts that needs to be understood when talking about how resource management is built up in terms of what to do stuff and how to do stuff?

Policies and mechanisms

What are policies when talking about resource management?

It is standards that must be followed by different implementations of the resource management system (e.g. what to do)

What is an example of a policy in resource management?

Scheduling algorithms

What are mechanisms when talking about resource management?

It is how stuff decided by a policy is actually performed (e.g. how to do). An example of this is context switching where you switch the executing process using hardware/software

What is an example of a mechanism in resource management?

A scheduling algorithm is designed and implemented in a specific way

What are some techniques that can be deployed to manage increasing complexity in OS'?

- Modularity

- Abstraction

- Layering

- Hierarchy

What is the core of the OS called?

Kernel

What is the kernel responsible for?

It is responsible for providing secure access to the hardware and executing programs. This includes:

- Process management

- Device driver

- Memory management

- System calls

What are system calls?

Interface between a running program and the kernel

What provides a system call interface?

Run-time libraries

What are some characteristics of a system call interface?

System calls are associated with a number each. It then maintains a table indexed according to these numbers.

What are some common types of OS structures?

- Monolithic kernel

- Microkernel

- Hybrid kernel

What is a monolithic kernel?

The entire OS works in kernel space

What are some pros and cons of a monolithic kernel?

Pros: Good isolation, security

Cons: Reliability, inflexibility

What is a microkernel?

The entire OS works in kernel space apart from some services and modules that are put in the user space

What are some pros and cons of a microkernel?

Pros: Reliability, security, flexibility

Cons: Complexity, communication overhead

What is a hybrid kernel?

A combination of a monolithic kernel and a microkernel

What OS structure does Linux use?

A monolithic kernel

What type of OS structure does Apple OSs and Windows use?

Hybrid kernel

What are some techniques that a OS uses in order to be efficient and convenient to use?

- Virtualization

- Concurrency

- Persistence

What is virtualization?

Creates virtual representations of a CPU, memory, disk, servers etc.

What is concurrency?

Events are occurring simultaneously and may interact with one another

What is persistence?

Safely storing data on different storage devices (hard drive, solid etc.)