1. Examples of Operating Systems.
What is an operating system?
Examples of Operating Systems.
OSX
Windows Mobile
Linux
Mac OS
Android (open handset alliance)
Unix
Windows XP
Windows 95
MS-DOS
Windows Vista
Symbian
Acorn MOS

2. What is an operating system?
What does it do?
Process Management
Memory management
I/O management
Support functions
Networking
User interface
Security

3. Instruction Set Architecture
Where does it fit in?
Application
Program
Instruction Level
Operating System
Implementation
Instruction Set Architecture
Micro architecture

4. Operating System Goals
Efficiency
Throughput
Functionality
Robustness
Extensibility
Portability
Security
Interactivity

5. Concepts Architectures of Operating Systems Increasing Efficiency
Monolithic
Layered
Kernel
Microkernel
Virtual Machines
Increasing Efficiency
Multi program
Multi User

6. Monolithic Architecture
Monolithic Architecture—the early operating systems
Every component is contained in the kernel, can directly communicate with other components

7. Monolithic Architecture
User Space
Applications
OS Layer
System Calls
Computer Hardware

8. Monolithic Architecture
Pros
Highly efficient – by direct intercommunication between components
Cons
difficult to develop
difficult to isolate the source of bugs and other errors
particularly susceptible to damage from malicious code

9. Layered Architecture Layered OS structure:
Group components that perform similar functions into layers. Each layer communicates only with neighbour layer
User Space
Kernel Space
Layer 3
Layer 2
Layer 1
Layer 0
Computer Hardware

10. Layered Architecture Pros Cons
It provides good modularity – helps simplify the development of an OS
Cons
Less efficient
Complex design – each functionality has to be divided into parts to fit into different layers.

11. Kernel Based Architecture
It separates the machine-independent parts from the machine-dependent parts
Kernel is machine-dependent. It contains the basic component of OS.
User Space
Operating System
OS Kernel
Computer Hardware

12. Kernel Based Architecture
Pros
Better portability—Kernel encloses all the machine-dependent code
Cons
Suffers similar problem as in layered OSs

13. Microkernel Based Architecture
As OS expanded, the kernel became large and difficult to manage
Microkernel approach removes all nonessential components from the kernel and implementing them as system and user-level programs.
Result: A smaller kernel

14. Microkernel Based Architecture
User Space
Operating System
Microkernel
Computer Hardware

15. Microkernel Based Architecture
Pros
Enhance portability, extensibility, reliability and security
Cons
Less efficient—increased system function overhead

16. Virtual Machines
Can create the illusion that there are more than one separate machines.
User Space
User Space
User Space
Kernel
Kernel
VM1
VM1
Virtual machine
implementation
Host Operating System
Computer Hardware

17. Increasing Efficiency
Multiprogramming
Try to Keep the CPU busy
CPU operations take less time than I/O
When a process waits for I/O operation, OS swaps to another process.
Operating
System
Job 1
Job 2
Job 3

18. Multi User
Logical extension of Multiprogramming