Operating Systems Flashcards
What is an operating system (OS)?
A program that controls the execution of application programs and acts as an interface between applications and the computer hardware
List the services provided by operating systems.
- File management
- Input/output management
- Process management
- Memory management
- Multiprocessor management
What is the most central part of an operating system?
The kernel
What is user mode in an operating system?
A mode where certain areas of memory are not accessible and certain instructions cannot be executed.
What is a mode switch?
A transition between user mode and kernel mode that is computationally expensive.
What are the four possible operating system structures?
- Monolithic
- Layered
- Microkernel
- Modular
Describe the monolithic structure of an operating system.
All services are implemented by a large kernel. Any new feature is added to the kernel.
What are the pros of the monolithic structure?
Communication within the kernel is fast.
What are the cons of the monolithic structure?
Difficult to understand, difficult to modify, and less secure.
If something goes wrong it goes really wrong
Describe the layered structure of an operating system.
Organizes services into distinct layers where each layer can only communicate with adjacent layers.
What are the pros of the layered structure?
Easy to debug and development can be organized into separate units.
What are the cons of the layered structure?
Performance may be poor due to multiple layers for service access.
Describe the microkernel structure of an operating system.
Services are implemented by servers, and a small kernel delivers messages between them.
What are the pros of the microkernel structure?
Secure and reliable.
What are the cons of the microkernel structure?
Performance may be poor due to increased communication overhead.
Describe the modular structure of an operating system.
Begins with a small kernel and adds or removes additional modules as needed.
What are the pros of the modular structure?
Fast since unnecessary services do not need to be loaded; allows for direct communication between modules.
What are the cons of the modular structure?
As the number of loaded modules increases, the OS begins to resemble a monolithic structure.
What are the objectives of an operating system (OS)
The objectives of an OS are to achieve convenience, efficiency, and the ability to evolve.
What does the functionality of the kernel depend on
The OS design
What is the kernel the subset of
Kernal is a subset of the operating system
When designing OS what do we want to minimise
Mode switches
What is the impact if something goes wrong in the user mode
Very limited impact as the application can only access its own memory and can’t interact with hardware directly
