1. Outline Introduction to Operating Systems Using the Operating Systems
The abstract model of computing
System calls

2. System Overview
A computer system consists of hardware and software that are combined to provide a tool to solve specific problems
Hardware includes CPU, memory, disks, printers, screen, keyboard, mouse ...
Software includes
System software
A general environment to create specific applications
Application software
A tool to solve a specific problem
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3. System Overview – cont.
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4. Hardware Resources Processor: execute instructions
Memory: store programs and data
Input/output (I/O)controllers: transfer to and from devices
Disk devices: long-term storage
Other devices: conversion between internal and external data representations
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5. Hardware Resources – cont.
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6. Hardware Interface – cont.
Everything that a programmer needs to know in order to write programs that perform desired operation on the hardware
Disk drive is an example
Disk interface provides functions to move disk head, transfer data
Monitor
Monitor interface provides functions to move the cursor, display characters/graphics
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7. Software Classification
System software
Provides a general programming environment in which programmers can create specific applications
Application software
Intended to solve a specific problem
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8. Software Classification - continued
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9. What is an Operating System?
The operating system is the part of the system software that manages the use of the hardware used by other system software and all application software
It is the system program that acts between the hardware and the user programs
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10. What is an Operating System? - continued
It provides services to user programs
Through system calls / message passing
File system services
Memory services
I/O services
It hides hardware from user programs
When your program shows a message on the monitor, it does not need to know the details
When your program generates a new file, it does not need to know where the free space is on your hard drive
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11. Differences between OS and System Software
Major differences between OS and general system software
OS abstracts the hardware directly
General system software relies on the abstractions provided by OS
OS provides the fundamental trusted mechanisms for resource sharing
A general purpose OS is domain-independent
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12. Operating System Functions
Resource manager
manage hardware and software resources
Resource abstraction and sharing
A nicer environment
implement a virtual machine for processes to run in
A program in execution is called a process
a nicer environment than the bare hardware
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13. Resource Management Functions
Transform physical resources to logical resources
Resource abstraction
Make the hardware resources easier to use
Multiplex one physical resource to several logical resources
Create multiple, logical copies of resources
Schedule physical and logical resources
Decide who gets to use the resources
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14. Resource Abstraction
Provides an abstract model of the operation of hardware components
Like data abstraction in Object-Oriented programming
Interface functions
Internal functions and status
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15. A Disk Device Abstraction
Three interface functions
Load(block, length, device)
seek(device, track)
out(device, sector)
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16. A Disk Device Abstraction – cont.
An abstract function for writing
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17. Resource Abstraction – cont.
Multi-level abstractions
Disk controller -> disk driver -> file system
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18. Resource Sharing Two types of sharing Time multiplexed sharing
time-sharing
schedule a serially-reusable resource among several users
Space multiplexed sharing
space-sharing
divide a multiple-use resource up among several users
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19. Time-multiplexing the Processor
- Called multiprogramming
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20. Time-multiplexing the Processor – cont.
- Resulted in concurrent execution or concurrency
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21. Time-multiplexing the Processor – cont.
- Multiprogramming can improve the overall system performance
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22. Space-multiplexing Memory
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23. Time-multiplexing I/O Devices
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24. Space-multiplexing the Disk
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25. Issues in Resource Sharing
Resource isolation and sharing
Protection
Sharing
Resource allocation
Scheduling
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26. Do We Need an OS? Not always But they are very useful
When resource abstraction or sharing is not needed
Some programs run “stand-alone”
Early computers did not have a sophisticated OS
OS was evolved along the hardware technology
But they are very useful
Reusable functions
Easier to use than the bare hardware
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27. Operating Systems Strategies
Several different strategies have been used
Earliest computers were dedicated to a single program and there was no multiprogramming and no OS
Batch systems
Timesharing systems
There are a few other recent strategies
Personal computers and workstations
Embedded systems
Small, communicating computers
Network technology
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28. Batch Processing Systems
Reduce setup time by batching similar jobs
Automatic job sequencing – automatically transfers control from one job to another. First rudimentary operating system.
Resident monitor
initial control in monitor
control transfers to job
when job completes control transfers back to monitor
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29. Batch Processing Systems - continued
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30. Memory Layout for a Simple Batch System
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31. Spooling
Overlap I/O of one job with computation of another job. While executing one job, the OS
Reads next job from card reader into a storage area on the disk (job queue).
Outputs printout of previous job from disk to printer.
Job pool – data structure that allows the OS to select which job to run next in order to increase CPU utilization
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32. Multi-programmed Batch Systems
Several jobs are kept in main memory at the same time, and the
CPU is multiplexed among them.
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33. OS Features for Multi-programming
I/O routine supplied by the system
Memory management – the system must allocate the memory to several jobs
CPU scheduling – the system must choose among several jobs ready to run
Allocation of devices
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34. Time-sharing Systems
The goal is to enable users to interact with the computer system
Batch processing systems do not allow user interactions
On-line communication between the user and the system is provided
When the operating system finishes the execution of one command, it seeks the next “control statement” not from a card reader, but rather from the user’s keyboard.
On-line system must be available for users to access data and code.
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35. Time-sharing Systems - continued
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36. Personal-computer Systems
Personal computers – computer system dedicated to a single user.
I/O devices – keyboards, mice, display screens, small printers.
User convenience and responsiveness.
Can adopt technology developed for larger operating system
often individuals have sole use of computer and do not need advanced CPU utilization of protection features.
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37. Personal-computer Systems - continued
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38. Embedded Systems
Often used as a control device in a dedicated application such as controlling scientific experiments, medical imaging systems, industrial control systems, and some display systems.
Well-defined fixed-time constraints.
Hard real-time system.
Secondary storage limited or absent, data stored in short-term memory, or read-only memory (ROM)
Conflicts with time-sharing systems, not supported by general-purpose operating systems.
Soft real-time system
Limited utility in industrial control or robotics
Useful in applications (multimedia, virtual reality) requiring advanced operating-system features.
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39. Parallel systems
Multiprocessor systems with more than one CPU in close communication.
Tightly coupled system – processors share memory and a clock; communication usually takes place through the shared memory.
Advantages of parallel system:
Increased throughput
Economical
Increased reliability
graceful degradation
fail-soft systems
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40. Distributed Systems
Distribute the computation among several physical processors
Loosely coupled system – each processor has its own local memory; processors communicate with one another through various communications lines, such as high-speed buses or telephone lines
Advantages of distributed systems
Resources Sharing
Computation speed up – load sharing
Reliability
Communications
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41. Distributed systems - cont.
Network operating system
provides file sharing
provides communication scheme
runs independently from other computers on the network
Distributed operating system
less autonomy between computers
gives the impression there is a single operating system controlling the network.
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42. Migration of Operating-System Concepts and Features
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43. Genesis of Modern OS
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44. Using the O.S.
For a programmer, the operating system interface is most important
The functions provided by the OS
Abstract resources that are available
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45. Requesting Services from O.S.
Two techniques
System call
Message passing
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46. Requesting Services – cont.
Two techniques
System call
Message passing
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47. System Call Interface System call interface
Operating system provides a set of operations called system calls
A programming interface
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48. How to Make a System Call
For a programmer
A system call is similar to a procedure/function call in a traditional programming language
System calls are available in C/C++ as library routines
For example, fork to create a new process
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49. How to Make a System Call – cont.
Do the parent and the child have the same sequence of instructions when fork() is successful?
Why do we say this is the child and this the parent?
How about here?
pid = fork();
if (pid == ((pid_t)-1)) {
// Something must be wrong with the fork
// error processing
} else {
if (pid == 0) {
// This is the child process
// This is the parent process }
//How about here, the parent or the child ?
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50. System Call Overview man –s 2 intro Process management system calls
List of all the system calls available
Process management system calls
Memory management system calls
File and I/O system calls
Communication system calls
Information maintenance system calls
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51. Process Management System Calls
fork – Create a new process
exit – Terminate a process
wait – Wait for a child process to terminate
exec – Execute a file
nice – Change scheduling priority for a process
_lwp_create – Create a new lightweight process
yield – Yield execution to another lightweight process
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52. Thread Related Functions and System Calls
POSIX Thread
pthread_create
pthread_join
pthread_exit
Solaris Thread
thr_create
thr_join
thr_exit
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53. Memory Management System Calls
brk – Change the size of data segment of process
memcntl – Memory management control
mmap – Map pages of memory
(Memory mapped I/O)
Note: malloc and free are library functions using memory management system calls
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54. File Management System Calls
open – Open a file for reading or writing
creat – Create a new file and open it
read – Read bytes from an open file
write – Write bytes to an open file
close – Close an open file
seek – Change the location in the open file of the next read or write
stat – Get information about a file
mkdir – Make a directory
mount – Mount a file system
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55. File Management System Calls
open – Open a file for reading or writing
creat – Create a new file and open it
read – Read bytes from an open file
write – Write bytes to an open file
close – Close an open file
seek – Change the location in the open file of the next read or write
stat – Get information about a file
mkdir – Make a directory
mount – Mount a file system
An open file is a dynamic object that can provide bytes from a file or accept bytes to be stored in the file. It has a set attributes, such as file pointer. It is a virtual device created by the operating system.
Files however are passive containers of data
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56. I/O System Calls open – Open a device for reading or writing
read – Read bytes from an open device
write – Write bytes to an open device
close – Close an open device
ioctl – Control device
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57. Communication System Calls
pipe – Create an inter-process channel
kill – Send a signal to a process or a group of processes
msgctl – Message control operations
shmat, shmctl, shmget, shmop – Shared memory operations
Semctl, semget, semop – Semaphore operations
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58. Information Maintenance System Calls
acct – Enable or disable process accounting
stime – Set system time and date
times – Get process and child process times
utimes – Set file times
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59. Interactive and Programming Interfaces
Interactive interfaces have advantages:
for exploration
for interactive use
Programming interfaces have advantages :
for detailed interactions
Inter-application programming
Scripting
It is useful for a program to have both interfaces
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60. Examples Shell System calls Interactive interface to OS
Programming interface to OS
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61. Shell as an Interactive Interface
Interactive access to the OS system calls and system and user programs
cd to change current working directory
System call is chdir
Started by the system for a user
Contains a simple programming language
Popularized by UNIX
Bourne shell, C shell (csh), Korn shell (ksh), Bourne-again shell (bash), etc.
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62. Two views of a shell
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63. Summary
Operating system is the system software that controls the basic operation of a computer
The layer between the hardware and the user programs
Resource manager: manage hardware and software resources
Goals of operating systems
Convenience for users by providing a wide range of functions
Efficient operation of the computer system
Operating system provides services to user programs through system calls
Shell as an interactive interface to system calls and system and user programs
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