OS + OS Design

Question 1

what is an os(what is their role)

Answer 1

Os: Manages hardware and system resources,
Shares out and accounts for resources,
Offers secure environment for applications,
Provides common device or I/O system

Question 2

The Operating system

Answer 2

• Includes kernel and system library interface

Question 3

Benefit of abstraction

Answer 3

The OS hides the complex hardware details and gives applications a simpler, cleaner interface to work with.
Hardware abstraction allows us to hide hardware
differences from Operating System– Operating System can then run on different hardware

Question 4

The OS provides abstract environments like:

Answer 4

Files instead of raw disk blocks

Processes/Threads instead of CPU register juggling

Memory allocations instead of managing physical RAM

System calls instead of direct hardware instructions

Question 5

different OS

Answer 5

Embedded/ Real-Time, emphasis on – Proven long term reliability and strict timing guarantees– Small footprint, no unnecessary code– Certification process for safety critical systems
* Server, emphasis on – Fairly sharing resources– Reliability
* Desktop, emphasis on
Could be same OS running
with different parameters– Interactivity– GUI and graphics/ media

Question 6

different OS

Answer 6

embedded/real time - can be found in cars, planes,etc.
Server - Web servers, databases
Desktop - Personal laptops , PC’s

Question 7

Design (OS) - Monolithic

Answer 7

Monolithic has a traditional approach (Tight coupling of non application code)
- All OS code running with full privileges
- Difficult to impose security or protection
- Efficient call structure(Shared access to resources)
- Difficult to maintain
(Code boundaries frequently blurred)

Question 8

Layered Approach

Answer 8

Realisation that we have identifiable layers in
system
- High-level components built on lower ones
- Impose tighter security as move from hardware
-Performance penalty with every layer crossed
Hard to manage if complex inter-layer call chain
Applications
* Can’t call up layers (only down) so needs thought at design

Question 9

Design OS(Micro kernel)

Answer 9

Minimal amount of code has ‘system’ privileges
* Most code in unprivileged ‘user space’
* Far more secure than other approaches
Components communicate by message passing
* Main function of kernel in this model is
Inter-Process Communication (IPC)
* Can be inefficient
* Most real implementations break model
- Extensible and have minimal system dependencies

Question 10

Modular OS

Answer 10

• Core kernel loads modules as needed
• Core relatively small
• More manageable, less scope for code problems
• Kernel modules run with elevated privileges
• Reliant on API and structure for kernel integrity
• Modules can still break things if they don’t follow rules
• Naturally restricted to module API
• Can access and share resources across modules