1. Operating System Overview
Tarek Abdelzaher
Lawrence Angrave
Vikram Adve
Copyright ©: Nahrstedt, Angrave, Abdelzaher

2. Today’s Objectives By the end of the hour you should be able to:
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Today’s Objectives By the end of the hour you should be able to:
Explain the main purpose of operating systems and describe milestones of OS evolution
Explain fundamental machine concepts such as:
Instruction processing,
Memory hierarchy,
Interrupts, and
I/O
Explain fundamental OS concepts such as:
System calls,
processes,
synchronization,
Files
Explain the POSIX standard (UNIX specification)

3. Copyright ©: Nahrstedt, Angrave, Abdelzaher
Today’s Applications
Application Software
Browser
Second Life
Yahoo
Chat Client
Pop Mail
Hardware
Network

4. Application Requirements
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Application Requirements
Application Software
Browser
Second Life
Yahoo
Chat Client
Pop Mail
Store
Read/write
Display
Print
Send/receive
Hardware
Network

5. Application Requirements
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Application Requirements
Application Software
Browser
Second Life
Yahoo
Chat Client
Pop Mail
Store
Read/write
Display
Print
Store
Read/write
Display
Print
Send/receive
Send/receive
Hardware
Network

6. Application Requirements
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Application Requirements
Application Software
Browser
Second Life
Yahoo
Chat Client
Pop Mail
Store
Read/write
Display
Print
Print
Store
Store
Send/receive
Read/write
Display
Print
Display
Send/receive
Send/receive
Read/write
Hardware
Network

7. Application Requirements
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Application Requirements
Application Software
Browser
Second Life
Yahoo
Chat Client
Pop Mail
Read/write
Store
Display
Print
Store
Print
Store
Store
Send/receive
Send/receive
Read/write
Display
Print
Display
Send/receive
Send/receive
Display
Read/write
Read/write
Print
Hardware
Network

8. Delegate Common Functions?
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Delegate Common Functions?
Application Software
Browser
Second Life
Yahoo
Chat Client
Pop Mail
Read/write
Store
Display
Print
Store
Print
Store
Store
Send/receive
Send/receive
Read/write
Display
Print
Display
Send/receive
Send/receive
Display
Read/write
Read/write
Print
Hardware
Network

9. Delegate Common Functions to an Operating System
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Delegate Common Functions to an Operating System
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Operating System
Read/Write
Standard
Output
Device
Control
File
System
Communication
Hardware
Network

10. OS Exports a Virtual Machine Interface
Copyright ©: Nahrstedt, Angrave, Abdelzaher
OS Exports a Virtual Machine Interface
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface (Virtual Machine)
Operating System
Read/Write
Standard
Output
Device
Control
File
System
Communication
Hardware
Network

11. Increase Portability = Minimize Machine-Specific Code
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Increase Portability = Minimize Machine-Specific Code
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface (Virtual Machine)
Operating System (machine independent part)
Read/Write
Standard
Output
Device
Control
File
System
Communication
Machine specific part
Hardware
Network

12. Increase Portability = Minimize Machine-Specific Code
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Increase Portability = Minimize Machine-Specific Code
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface (Virtual Machine)
Operating System (machine independent part)
Portable
Read/Write
Standard
Output
Device
Control
File
System
Communication
Machine specific part
Hardware
Network

13. OS Runs on Multiple Platforms while Presenting same Interface
Copyright ©: Nahrstedt, Angrave, Abdelzaher
OS Runs on Multiple Platforms while Presenting same Interface
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface (Virtual Machine)
Operating System (machine independent part)
Portable
Read/Write
Standard
Output
Device
Control
File
System
Communication

14. OS Runs on Multiple Platforms while Presenting same Interface
Copyright ©: Nahrstedt, Angrave, Abdelzaher
OS Runs on Multiple Platforms while Presenting same Interface
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
Standard Operating System Interface (Virtual Machine)
Operating System (machine independent part)
Portable
Read/Write
Standard
Output
Device
Control
File
System
Communication
Machine specific part
Hardware
Network

15. POSIX – The UNIX Interface Standard
Copyright ©: Nahrstedt, Angrave, Abdelzaher
POSIX – The UNIX Interface Standard
Application Software
Web Server
Second Life
Yahoo
Chat
Pop Mail
The POSIX Standard Specifies UNIX Interface
Operating System (machine independent part)
Portable
Read/Write
Standard
Output
Device
Control
File
System
Communication
Machine specific part
Hardware
Network

16. A peek into Unix Application Libraries User space/level
Copyright ©: Nahrstedt, Angrave, Abdelzaher
A peek into Unix
Application
Libraries
User space/level
Kernel space/level
Portable OS Layer
Machine-dependent layer
User/kernel modes are supported by hardware
Some systems do not have clear user-kernel boundary

17. Unix: Application Application (E.g., emacs) Libraries
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Unix: Application
Application (E.g., emacs)
Written by programmer
Compiled by programmer
Uses function calls
Libraries
Portable OS Layer
Machine-dependent layer

18. Unix: Libraries Application Libraries (e.g., stdio.h)
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Unix: Libraries
Application
Provided pre-compiled
Defined in headers
Input to linker (compiler)
Invoked like functions
Libraries (e.g., stdio.h)
Portable OS Layer
Machine-dependent layer

19. Typical Unix OS Structure
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Typical Unix OS Structure
Application
Libraries
Machine-dependent layer
Portable OS Layer
system calls (read, open..)
All “high-level” code

20. Typical Unix OS Structure
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Typical Unix OS Structure
Application
Bootstrap
System initialization
Interrupt and exception
I/O device driver
Memory management
Kernel/user mode switching
Processor management
Libraries
Portable OS Layer
Machine-dependent layer

21. Summary: What is an Operating System?
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Summary: What is an Operating System?
It is an extended machine
Hides the messy details which must be performed
Presents user with a virtual machine, easier to use
It is a resource manager
Each program gets time with the resource
Each program gets space on the resource

22. History of Operating Systems
Copyright ©: Nahrstedt, Angrave, Abdelzaher
History of Operating Systems
Early systems
bring cards to 1401
read cards to tape
put tape on 7094 which does computing
put tape on 1401 which prints output
Batch  Multiprogramming  Time sharing  Personal

23. History of Operating Systems
Copyright ©: Nahrstedt, Angrave, Abdelzaher
History of Operating Systems
Structure of a typical job – 2nd generation

24. History of Operating Systems
Copyright ©: Nahrstedt, Angrave, Abdelzaher
History of Operating Systems
Multiprogramming/timesharing system
three jobs in memory – 3rd generation

25. History of Operating Systems
Copyright ©: Nahrstedt, Angrave, Abdelzaher
History of Operating Systems
Memory
Management
Process
Management
Multiprogramming/timesharing system
three jobs in memory – 3rd generation

26. History of Computer Generations
Copyright ©: Nahrstedt, Angrave, Abdelzaher
History of Computer Generations
First generation 1945 – 1955
vacuum tubes, plug boards
Second generation
transistors, batch systems
Third generation – 1980
ICs and multiprogramming
Fourth generation 1980 – present
personal computers

27. Computer Hardware Review
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Computer Hardware Review
Bus
Components of a simple personal computer

28. Computer Hardware Review
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Computer Hardware Review
CPU
Bus
Components of a simple personal computer

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CPU
Fetch instruction from code memory
Fetch operands from data memory
Perform operation (and store result)
Go to next instruction

30. Copyright ©: Nahrstedt, Angrave, Abdelzaher
CPU Registers
Fetch instruction from code memory
Fetch operands from data memory
Perform operation (and store result)
Go to next instruction
Note: CPU must maintain certain state
Current instructions to fetch (program counter)
Location of code memory segment
Location of data memory segment

31. Copyright ©: Nahrstedt, Angrave, Abdelzaher
CPU Register Examples
Hold instruction operands
Point to start of
Code segment
Data segment
Stack segment
Point to current position of
Instruction pointer
Stack pointer

32. Code Layout for Process
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Code Layout for Process
Processes have three segments: text, data, stack

33. Copyright ©: Nahrstedt, Angrave, Abdelzaher
Memory Hierarchy
Typical memory hierarchy
numbers shown are rough approximations (old generation of computers)

34. Computer Hardware Review
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Computer Hardware Review
CPU
Memory
Bus
Components of a simple personal computer

35. Computer Hardware Review
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Computer Hardware Review
CPU
Memory
I/O
Devices
Bus
Components of a simple personal computer

36. Computer Hardware Review Example I/O Device: Disk
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Computer Hardware Review Example I/O Device: Disk
Structure of a disk drive

37. Example of modern architecture
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Example of modern architecture
Graphics Processor
MPEG
Comp.
Digital Video
Copper Fibre Channel
Network Interface
Fibre Channel
Network
Interface
IEEE 1394
Discrete IO IO
CPU+Multi-
Level Cache
PCI Bus 0a
PCI Bus 1a
Shared
Memory
Ethernet
RS-485
PCI Bus 0b
PCI Bus 1b
System
Controller
Power PC 1000 MHz
64 Bit Wide Memory Bus
256 MB DDR SDRAM
125 MHz
64 Bit PCI-X
100 MHz
32 Bit PCI
66 MHz
33 MHz
PCI to PCI Bridge
PCI-X to PCI Bridge
Port 1
Port 2
Inactive

38. Interrupts
CPU hardware has the interrupt report line that the CPU senses after executing each instruction
Why interrupts?
Real life analogy for interrupts
An alarm sets off when the food/laundry is ready
You can do other things in between and handle the event once notified

39. Operating System Review: Processes
Copyright ©: Nahrstedt, Angrave, Abdelzaher
Operating System Review: Processes
A process tree
A created two child processes, B and C
B created three child processes, D, E, and F

40. Copyright ©: Nahrstedt, Angrave, Abdelzaher
Context Switching
How would you switch CPU execution from one process to another?

41. Semaphores (synchronization)
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Semaphores (synchronization)
Control access to shared resources (like shared data structures)
Prevent race conditions, synchronize access to shared resources.
Needed for concurrent programming (we will discuss a lot about this topic)

42. Copyright ©: Nahrstedt, Angrave, Abdelzaher
Why Synchronization?
Processes and threads can be preempted at arbitrary times, which may generate problems.
Example: What is the execution outcome of the following two threads (initially x=0)?
Thread 1:
Read X
Add 1
Write X
Thread 2:
Read X
Add 1
Write X 42

43. Copyright ©: Nahrstedt, Angrave, Abdelzaher
Why Synchronization?
Example: What is the execution outcome of the following two threads (initially x=0)?
Depending on the execution order of thread 1 and 2, the outcome can be x=1 or x=2.
Thread 1:
Read X
Add 1
Write X
Thread 2:
Read X
Add 1
Write X 43

44. Inter-process Communication
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Inter-process Communication
Two processes connected by a pipe