1. Chapter 1 Introduction to Operating System
Bernard Chen
Spring 2007

2. Outline 1.1 What is OS 1.2 Computer System Organization
1.3 Computer System Architecture
1.4 OS Structure
1.5 OS Operations
Process, Memory, Storage management
1.9 Protection and Security
1.10~ Systems

3. 1.1 What is Operating System?
An operating system is a program that manages the computer hardware.
It also provides a basis for application programs and acts as an intermediary between the computer user and computer hardware.

4. What do Operating System do?
The computer system can be divided roughly into four components:
The hardware
The operating system
The application software
The Users

6. USER View of OS Ease to use (Home PCs) Efficient resource utilization
(Work stations)

7. SYSTEM view of OS OS is a resource allocator
Manages all resources (CPU time, memory
space, storage space, I/O and so on)
Decides between conflicting requests for
efficient and fair resource use
OS is a control program
Controls execution of programs to prevent
errors and improper use of the computer

8. 1.2 Computer System Organization
Basic Organization
Storage Structure
I/O structure

9. Computer Startup Bootstrap program is loaded at power up or reboot
Typically stored in ROM, generally known as firmware
Initialize all aspects of system
Loads operating system kernel and starts execution

10. 1.2.1 Computer System Organization

11. 1.2.1 Computer System Organization
I/O devices and the CPU can execute concurrently.
Each device controller is in charge of a particular device type.
Each device controller has a local buffer.

12. Interrupt Timeline

13. 1.2.2 Storage Structure Main Memory:
Main memory is the only large storage media that the CPU can access directly
Main memory is usually too small to store all needed programs and data
Main memory is a volatile storage device that loses its contents when power is off

14. 1.2.2 Storage Structure
Therefore, most computer provide secondary storage as extension to store web browser, compliers, word processors…etc

15. Storage Device Hierarchy

16. 1.2.2 Storage Structure Storage systems organized in hierarchy. Speed
Cost
Volatility
Caching–copying information into faster storage system; main memory can be viewed as a last cache for secondary storage.

17. Performance of Various Levels of Storage

18. Caching
Information in use copied from slower to faster storage temporarily
Important principle, performed at many levels in a computer (in hardware, operating system, software)

19. Caching
Faster storage (cache) checked first to determine if information is there
If it is, information used directly from the cache (fast)
If not, data copied to cache and used there
Cache is usually smaller than storage being cached
Cache management is an important design problem
Cache size and replacement policy

20. 1.3 Computer-System Architecture
1.3.1 Single-Processor Systems
1.3.2 Multiprocessor Systems
1.3.3 Cluster Systems

21. 1.3.1 Single-Processor Systems
On a single processor system, there is only one main CPU capable of executing a general purpose instruction set.
Some other special-purpose processors may also included. Such as:
GPU
Disk-controller microprocessor
Keyboard microprocessor

22. 1.3.2 Multiprocessor Systems
Also called Parallel Systems
Advantages:
Increase throughput
Economy of scale
Increase reliability (fault tolerant)

23. 1.3.2 Multiprocessor Systems
Two types of multiprocessor systems:
1. Asymmetric multiprocessing
(master and slave processors)
2. Symmetric multiprocessing
(Shared memory system)

24. 1.3.3 Clustered Systems
Clustered computers share storage and are closely linked via Local-area network (LAN) or a faster interconnection.

25. 1.4 OS Architecture
One of the most important aspect of OS is the ability to Multiprogramming
Single user cannot keep CPU and I/O devices busy at all times
One job selected and run via job scheduling
When it has to wait (for I/O for example), OS switches to another job

26. Memory Layout for Multiprogrammed System

27. Multiprogramming Jobs are stored in “Job Pool”
Virtual memory is the useful technique for the limitation size of physical memory

28. 1.5 OS operations Interrupt (driven by hardware) vs.
Trap (called by software or error)
Trap example: divide by 0; invalid memory access
We need to make sure that an error in a user program could cause problems only for the one program that was running (such as infinite loop)

29. Dual Mode Operation
Dual-mode operation allows OS to protect itself and other system components
It contains user mode (mode bit:1) and Kernel mode (mode bit:0)
The operating system loaded user application starts in user mode. Whenever a trap or interrupt occurs, hardware switches to kernel mode.

30. Transition from user to kernel mode

31. C library handling of write()
#include<stdio.h>
Int main() { …
printf(“hellow world”); }
User mode
Standard C library
Kernel mode
Write() system call

32. Dual Mode Operation
Privileged instructions: some machine instructions that may cause harm, can only be executed in kernel mode.
Such as instruction switch to user mode; I/O control; timer management, and interrupt management.

33. Timer To prevent the OS out of control by CPU
Set interrupt after specific period
Operating system decrements counter
When counter zero generate an interrupt
Set up before scheduling process to regain control or terminate program that exceeds allotted time

34. Process management
A process is a program in execution. It is a unit of work within the system.
Process needs resources to accomplish its task CPU, Memory, files, I/O devices
Process termination requires reclaim of any reusable resources

35. Process management
Single-threaded process has one program counter (PC) specifying location of next instruction to execute
Process executes instructions sequentially, one at a time until completion
Multi-threaded process has one program counter per thread

36. Process management
The operating system is responsible for the following activities in connection with process management:
Creating and deleting both user and system processes (Ch3)
Suspending and resuming processes (Ch5)
Providing mechanisms for process synchronization (Ch6)
Providing mechanisms for process communication (Ch4)
Providing mechanisms for deadlock handling(ch7)

37. Memory Management All data in memory before and after processing
All instructions in memory in order to execute
Memory management determines what is in memory when optimizing CPU utilization and computer response to users

38. Memory management activities
Keeping track of which parts of memory are currently being used and by whom
Deciding which processes and data to move into and out of memory
Allocating and deallocating memory space as needed

39. Storage Management
OS provides uniform, logical view of information storage
file
Each medium is controlled by device (i.e., disk drive, tape drive)

40. Storage Management File-System management
Files usually organized into directories
Access control on most systems to determine who can access what
OS activities include
Creating and deleting files and directories
Primitives to manipulate files and dirs
Mapping files onto secondary storage
Backup files onto stable (non-volatile) storage media

41. Mass Mass-Storage Management
Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time.
OS activities
Free-space management
Storage allocation
Disk scheduling
Tertiary storage includes optical storage, magnetic tape
Varies between WORM (write-once, read-many-times) and RW (read-write)

42. Protection and Security
Protection–any mechanism for controlling access of processes or users to resources defined by the OS (Ch14)
Security–defense of the system against internal and external attacks even when protection is activated (Ch15)
(including denial-of-service, worms, viruses, identity theft, theft of service)

43. Protection and Security
Systems generally first distinguish among users, to determine who can do what
User identities (user IDs, security IDs) include name and associated number, one per user
User ID then associated with all files, processes of that user to determine access control
Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file
Privilege escalation allows user to change to effective ID with more rights

44. Computing Environments
Traditional computer
Used to be single system, then modems
Now firewalled, networked

45. Client-Server computing
Many system now servers, responding request to clients

46. Peer Peer-to to-Peer Computing
Another model of distributed system
P2P does not distinguish clients and servers
Instead all nodes are considered peers
May each act as client, server or both
Node must join P2P network

47. Web-Based computing Web has become ubiquitous
More devices becoming networked to allow web access, such as work stations, PDA, even cell phone

48. Operating System Services
User interface
Program execution
File-system manipulation
Communication
Error detection
Resource allocation
Accounting
Protection and security