1 Operating System Overview

2 Today’s Objectives 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 Today’s Applications BrowserSecond Life Yahoo Chat Client Pop Mail Application Software HardwareNetwork

4 Application Requirements BrowserSecond Life Yahoo Chat Client Pop Mail Application Software HardwareNetwork Read/write Display Print Store Send/receive

5 BrowserSecond Life Yahoo Chat Client Pop Mail Application Software HardwareNetwork Read/write Display Print Store Read/write Display Print Store Send/receive Application Requirements

6 BrowserSecond Life Yahoo Chat Client Pop Mail Application Software HardwareNetwork Read/write Display Print Store Read/write Display Print Store Send/receive Read/write Display Print Store Send/receive Application Requirements

7 BrowserSecond Life Yahoo Chat Client Pop Mail Application Software HardwareNetwork Read/write Display Print Store Read/write Display Print Store Send/receive Read/write Display Print Store Send/receive Display Store Print Read/write Application Requirements

8 Delegate Common Functions? BrowserSecond Life Yahoo Chat Client Pop Mail Application Software HardwareNetwork Read/write Display Print Store Read/write Display Print Store Send/receive Read/write Display Print Store Send/receive Display Store Print Read/write

9 Delegate Common Functions to an Operating System Web ServerSecond Life Yahoo Chat Pop Mail Application Software Operating System NetworkHardware Read/Write Standard Output Device Control File System Communication

10 OS Exports a Virtual Machine Interface Web ServerSecond Life Yahoo Chat Pop Mail Application Software Operating System NetworkHardware Read/Write Standard Output Device Control File System Communication Standard Operating System Interface (Virtual Machine)

11 Increase Portability = Minimize Machine-Specific Code Web ServerSecond Life Yahoo Chat Pop Mail Application Software Network Hardware Machine specific part Read/Write Standard Output Device Control File System Communication Operating System (machine independent part) Standard Operating System Interface (Virtual Machine)

12 Web ServerSecond Life Yahoo Chat Pop Mail Application Software Network Hardware Machine specific part Read/Write Standard Output Device Control File System Communication Operating System (machine independent part) Standard Operating System Interface (Virtual Machine) Portable Increase Portability = Minimize Machine-Specific Code

13 Web ServerSecond Life Yahoo Chat Pop Mail Application Software Read/Write Standard Output Device Control File System Communication Operating System (machine independent part) Standard Operating System Interface (Virtual Machine) Portable OS Runs on Multiple Platforms while Presenting same Interface

14 Web ServerSecond Life Yahoo Chat Pop Mail Application Software Network Hardware Machine specific part Read/Write Standard Output Device Control File System Communication Operating System (machine independent part) Standard Operating System Interface (Virtual Machine) Portable OS Runs on Multiple Platforms while Presenting same Interface

15 POSIX – The UNIX Interface Standard Web ServerSecond Life Yahoo Chat Pop Mail Application Software Network Hardware Machine specific part Read/Write Standard Output Device Control File System Communication Operating System (machine independent part) The POSIX Standard Specifies UNIX Interface Portable

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

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

18 Unix: Libraries Application Portable OS Layer Libraries (e.g., stdio.h) Machine-dependent layer Provided pre-compiled Defined in headers Input to linker (compiler) Invoked like functions May be “resolved” when program is loaded

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

20 Typical Unix OS Structure Application Portable OS Layer Libraries Machine-dependent layer Bootstrap System initialization Interrupt and exception I/O device driver Memory management Kernel/user mode switching Processor management

21 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 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 Structure of a typical job – 2 nd generation

24 History of Operating Systems Multiprogramming/timesharing system – three jobs in memory – 3 rd generation

25 History of Operating Systems Multiprogramming/timesharing system – three jobs in memory – 3 rd generation Memory Management Process Management

26 History of Computer Generations First generation 1945 – 1955 vacuum tubes, plug boards Second generation transistors, batch systems Third generation 1965 – 1980 ICs and multiprogramming Fourth generation 1980 – present personal computers

27 Computer Hardware Review Components of a simple personal computer Bus

28 Large Pentium system

29 Computer Hardware Review Components of a simple personal computer Bus CPU

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

31 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

32 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

33 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 Why stack?

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

35 Code Layout for Process Processes have three segments: text, data, stack Where is this stored?

36 Computer Hardware Review Components of a simple personal computer Bus CPUMemory

37 Memory Hierarchy Typical memory hierarchy – numbers shown are rough approximations

38 Computer Hardware Review Components of a simple personal computer Bus CPUMemory I/O Devices

39 I/O Interrupt Mechanism (a) a) Steps in starting an I/O device and getting interrupt b) How the CPU is interrupted (b)

40 Computer Hardware Review Example I/O Device: Disk Structure of a disk drive

41 Operating System Review: Processes A process tree A created two child processes, B and C B created three child processes, D, E, and F

42 Context Switching How would you switch CPU execution from one process to another?

43 Semaphores Control access to resources

44 Shared Resources, Conflicts, and Deadlocks (a) A potential deadlock. (b) an actual deadlock.

45 Inter-process Communication Two processes connected by a pipe