Outline

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

3
System Overview cont.
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

5
Hardware Resources cont.
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

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

8
Software Classification - continued
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

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

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

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

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

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

15
A Disk Device Abstraction

• Three interface functions
• Load(block, length, device)
• seek(device, track)
• out(device, sector)

16
A Disk Device Abstraction cont.

• An abstract function for writing

17
Resource Abstraction cont.

• Multi-level abstractions
• Disk controller -gt disk driver -gt file system

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

19
Time-multiplexing the Processor
- Called multiprogramming
20
Time-multiplexing the Processor cont.
- Resulted in concurrent execution or concurrency
21
Time-multiplexing the Processor cont.
- Multiprogramming can improve the overall system
performance
22
Space-multiplexing Memory
23
Time-multiplexing I/O Devices
24
Space-multiplexing the Disk
25
Issues in Resource Sharing

• Resource isolation and sharing
• Protection
• Sharing
• Resource allocation
• Scheduling

26
Do We Need an OS?

• Not always
• 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

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

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

29
Batch Processing Systems - continued
30
Memory Layout for a Simple Batch System
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

32
Multi-programmed Batch Systems
Several jobs are kept in main memory at the same
time, and the CPU is multiplexed among them.
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

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 users keyboard.
• On-line system must be available for users to
  access data and code.

35
Time-sharing Systems - continued
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.

37
Personal-computer Systems - continued
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.

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

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

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.

42
Migration of Operating-System Concepts and
Features
43
Genesis of Modern OS
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

45
Requesting Services from O.S.

• Two techniques
• System call
• Message passing

46
Requesting Services cont.

• Two techniques
• System call
• Message passing

47
System Call Interface

• System call interface
• Operating system provides a set of operations
  called system calls
• A programming interface

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

49
How to Make a System Call cont.

• 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
• ........
• else
• // This is the parent process
• .........
• //How about here, the parent or the child ?
• ...........

50
System Call Overview

• man s 2 intro
• 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

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

52
Thread Related Functions and System Calls

• POSIX Thread
• pthread_create
• pthread_join
• pthread_exit
• Solaris Thread
• thr_create
• thr_join
• thr_exit

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

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

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
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

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

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

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

60
Examples

• Shell
• Interactive interface to OS
• System calls
• Programming interface to OS

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.

62
Two views of a shell
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