Chapter 1 Introduction. 2 Outline What is an operating system? History of operating systems...

Chapter 1Introduction

2

Outline

• What is an operating system?

• History of operating systems

• Categories of operating systems

• Computer hardware review

• Operating system concepts

• System calls

• Operating system structure

3

Computer As A Complex System

• Many resources– Hardware: processors, memory, disks, printers,

keyboard, display, network interfaces, …– Software: office tools, multimedia players, …

• Many tasks– Surfing web, handling emails, solving equations,

playing music, …

• Many users– Playing with computer should be easy

4

Read From Diskette …

• Basic commands: read and write– 13 parameters, packed into 9 bytes

• Controller chips– 23 status and error field

• Motor switch: on/off– Don’t leave motor on too long!

• Do you want to program the hardware directly?– A simpler interface is needed!

5

Why A Simple Interface Possible?

• Many tedious details can be handled by default– They are out of the user’s interest

• Only some key features are important– Examples: file name, length of the file, etc

• A simple interface– Present key features to programmer– Hide many tedious details– Meet requirements from many programs

6

OS As An Extended Machine

• Extended machine/virtual machine– Easier to program than the underlying hardware– Provide a variety of services (system calls)

• Trade-off– Higher efficiency in program development and

system management– Less efficiency in program execution

7

Programs Without Coordination

• Three programs want to output to a printer– A chaos if no coordination

• How to coordinate?– Buffer outputs on disk– Copy complete outputs to printer one by one

• Do you want to coordinate everything in a computer system?– A resource manager is needed!

8

OS As A Resource Manager

• Multiplexing (sharing) resources– In time

• Users/programs take turns using resources• CPU, printers, etc.

– In space• Users/programs get parts of resources• Main memory, disk, etc.

• Issues about a good manager– Fairness, efficiency, protection, …

9

What Is An Operating System?Provide user programs with a simpler interface

Manage resources

Banking system

Airline reservation

Web browser

Application programs

Compilers EditorsCommand interpreter System

programsOperating system

Machine language

HardwareMicroarchitecture

Physical devices

10

Outline






• System calls


11

History of Operating Systems

• OS and architecture of computers– Computer evolves so does OS– To provide better service OS has impact on

computer design

• Keep evolving through years– Four generations so far

12

The First Generation Computer

• Vacuum tubes and plugboards– 1944-1955

• Applications: – Straightforward numerical calculations

• Scenario– Single group of people designed, built,

programmed, operated and maintained a machine

– All in absolute machine language• No operating system

– The people maintaining the computers are OS?!

13

The Second Generation OS

• Transistors and batch systems– 1955-1965

• Applications– Scientific and engineering calculation

IBM 1401 IBM 7094 IBM 1401

Cards from programmers

Read batch of jobs onto tape

Input tape

Do computing

Output tape

Print out

14

Ancestor of Today’s OS

• Scenario: batch systems– Fortran

• Operating system– Read a job from tape run the job write

output onto a second tape

– Load next job

• Examples: – FMS, IBSYS

15

The Third Generation OS

• Features: ICs and multiprogramming– 1965-1980

• Applications– Numerical calculations in science & engineering

• Word-oriented, large-scale scientific computers

– Massive commercial data processing• Character-oriented, commercial computers

– Can we solve both problems at a single stroke?

16

System/360 and OS/360

• One family

– A series of software-compatible machines

– Different only in price and performance

– Capable of both scientific & commercial apps

• Problems

– Dinosaurs: huge operating systems

– Millions of instructions, thousands of developers

17

Key Advances in 3rd Gen OS

• Multiprogramming– Run job 2 while job 1 waiting for I/O– Keep CPU busy

• Spooling– Read job from cards to disk asap– Load new jobs from disk whenever old job done

• Time sharing– CPU is allocated in turn

18

Milestones

• IBM OS/360• M.I.T. CTSS• M.I.T. MULTICS• Ken Thompson UNIX

– AT&T UNIX System V– UC Berkeley UNIX BSD– IEEE POSIX– Andrew S. Tanenbaum MINIX– Linus Torvalds Linux

19

The Fourth Generation OS

• Personal computers– 1980-now– An individual has her own computer

• Milestones– Kildall CP/M for Intel 8080, Z80– MS-DOS/BASIC for IBM PC– Engelbart GUI– MS Windows, Windows NT– UNIX X Windows– Network & distributed operating systems

20

Outline






• System calls


21

Categories of Operating Systems

• Mainframe operating systems

• Server operating systems

• Multiprocessor operating systems

• Personal computer operating systems

• Real-time operating systems

• Embedded operating systems

• Smart card operating systems

22

Mainframe Operating Systems

• Why mainframe computers– Strong I/O capability, e.g., 1000 disks, TB space– High-end servers

• Features of OS– Batch– Transaction processing– Timesharing

• Example: IBM OS/390

23

Server Operating Systems

• Hardware platforms– Very large personal computers or workstations

• Services– Printing– File accessing– Web

• Examples– UNIX, Windows 2000, Linux

24

Multiprocessor Operating Systems

• Multiple CPUs within a single system– Parallel computers: loosely coupled– Multi-computers: tightly coupled– Multiprocessors: share memory

• Features of OS– Communications and connectivity– Variations of the server operating systems

25

Personal Computer OS

• Good interface to a single user– Word processing, spreadsheets, internet

access, …

• Examples– Windows 98, Windows 2000– Macintosh operating system– Linux

26

Real-time Operating Systems

• Having time as a key parameter– Industrial process control systems

• Hard/soft real-time systems– Hard real-time system: actions absolutely must

occur at a certain moment• Robot at an assembly line

– Soft real-time system: missing an occasional deadline is acceptable

• Digital audio or multimedia systems

27

Embedded Operating Systems

• Very small computers– Palmtop/PDA– Device controllers

• Features of OS– Kind of real-time systems– Restrictions in size, memory, power, …

• Example: PalmOS, Windows CE

28

Smart Card Operating Systems

• CPU chips on credit card-sized devices– Proprietary systems

• Features– Java oriented– Multiprogramming for Java applets– Resource management and protection

29

Outline






• System calls


30

Components of a Computer

• System bus: connect all components

Bus

CPU MemoryVideo

controllerKeyboard controller

Floppy disk

controller

Hard disk controller

Monitor Keyboard

Floppy disk

driver

Hard disk

driver

31

CPU

• Registers– General registers– Program counter: pointer to next instruction– Stack pointer: to the top of current memory– PSW: condition code bits

• Basic model– Fetching instruction decoding executing

• Execution image: a snapshot of registers

32

• Pipeline: overlap instruction execution

• Superscalar: multiple execution units

Execute unit

Decode unit

Fetch unit

Pipeline and Superscalar

I1

I2

I3

Fetch unit

Decode unit

Fetch unit

Decode unit

Holding buffer

Execute unit

Execute unit

Execute unit

33

System Calls

• Two modes in CPU– Kernel mode: full capability– User mode: disallow I/O, memory protection

• System calls: get OS service for user program– Traps: OS gets control– TRAP instruction switches from user mode to

kernel mode and starts OS– When the work done, control is returned to user

program

34

Memory Hierarchy

Typical access time

Typical capacity

1 nsec Register <1 KB

2 nsec Cache 1 MB

10 nsec Main memory 64-512 MB

10 msec Magnetic disk 5-50 GB

100 sec Magnetic tape 20-100 GB

35

Nonvolatile RAM

• ROM– Programmed once, cannot be changed

afterward– Fast and inexpensive– Boot strap loader, fixed programs

• EEPROM and flash RAM– Rewritable

• CMOS– Volatile, one battery lasts for several years

36

Memory Management

• Hold multiple programs in main memory– Improve CPU utilization

• Problems– Protection

• Program A is not allowed to fetch data within program B

– Relocation• Each program starts from logical address 0• How to load and allocate them into main memory?

37

Base/limit Registers• Base register

– Point to the start of a program– Its content is added to every program

address• Limit register

– Record the size of program + data– Limit of addresses

• Virtual address physical address– Base = 4096, limit = 6114– Virtual addr = 2000 physical addr =

6096 < limit, legal!• MMU: memory management unit

User program and data

User program and data

Operating system

0

Base

Limit

0xFFFFFFF

38

Split Program and Data

• Why: multiple users may run a same program

• How: base/limit registers for program and data, respectively

• Overhead of switching: context switch

User-2 data

User program

User-1 data

Operating system

Base-2

Limit-2

Registers when

running program 1

Base-1

Limit-1

Base-2

Limit-2

Registers when

running program 2

Base-1

Limit-1

39

I/O Devices

• Controller: physically controls the devices– Devices are diverse and complicated

• Device driver: software talks to a controller– Depends on operating systems

• Installation of drivers– Relink kernel with new driver, reboot

– Register driver in system file, reboot

– Install on-the-fly, NO rebootdevice

controller

driver

Operating system

40

Busy Waiting I/OUser program Kernel Driver I/O device

Issue a system call

Call driver

Start I/O

Polling Do I/O

Put data

Return control to

caller

Continue

41

I/O by Interrupt• Driver programs controller by writing its device registers.

Controller starts device• Controller finishes reading/writing, and then signals the

interrupt controller• If interrupt controller can accept the interrupt, it informs

CPU• Interrupt controller puts the number of device on the bus,

CPU read it

CPU Interrupt controller Disk controller

Disk drive

12

34

42

Interrupt Processing

Current instruction

Next instruction

Interrupt handler

1. Interrupt

2. Dispatch to handler

3. Return

43

Direct Memory Access (DMA)User program Kernel I/O device & memory

Issue a system call

Set up DMA chip

SuspendedRun other

programsI/O directly

Issue interrupt when

finish

Set the program

status as “ready”

Ready to continue

44

Advanced Computer With Multiple Buses

IDE bus

SCSI bus

USB bus

Level 2 cache CPU

PCI bridge

Main memory

Cache bus Local bus Memory bus

PCI bus

Available PCI slotSCSI USB ISA

bridge IDE disk

Graphics adaptor

MonitorISA busMouse Keyboard

Modem Sound card PrinterAvailable ISA slot

45

Plug and Play

• Problems without plug and play– Each I/O card has a fixed interrupt level/address– When new card comes conflict level/address– Use switches/jumpers to select good

level/address more than an art

• How plug and play– System collects info/assign level/address for I/O

devices– BIOS does major work

46

Warm-up

• Operating system = extended (virtual) machine + resource manager

• Hardware evolving operating system evolving– 4 generations– Various hardware platform various OS

• Important components of a computer– CPU, bus, memory, I/O

47

Outline






• System calls


48

Process

• A program in execution– Address space: a list of memory locations the

process can read/write– Registers, e.g., PC, SP, …

• Examples– Two processes running two programs: Word,

Excel– Two processes running the same program:

multiple web-browsers in a PC

49

Information About Processes

• Process table in operating systems– Registers, etc.

• Core image: suspended process address space

• Process information = Process table entry + core image

50

Process Management System Calls• Create a new (child) process

– Process tree

• Interprocess communication– Communication– Synchronization

• Request/release memory

• Alarm signal– E.g., remote communication

A

B C

D E F

51

Users and Processes

• User group: a group of users– GID

• Users are identified by UID– Superuser/system administrator

• One user can run many processes– Processes from one user share same UID– Processes are identified by PID

52

Deadlocks No one can make any progress!

53

Deadlock in ComputerTime Process 1 Process 2

1 Get CD-recorder

2 Get tape drive

3 Wait for tape drive

4 Wait for CD recorder

Deadlock!

Process 1Process 2

54

Memory Management

• Sharing main memory among processes– Protection

• Handling virtual memory larger than physical memory– Reallocation: map memory space to main

memory and disk

55

Files and Directories

• Directory: hierarchy of filesRoot

Students

Robert Matty Leo

Faculty

Prof. Brwon Prof. Green Prof. White

Courses Papers Grants Committees

CS101 CS105Path /Faculty/Prof.Brown/Courses/CS105

56

Mounted File SystemRoot

a b

c d

Floppy

x y

Root

a b

c d x y

57

Model I/O Devices As Files

• Block special files: a collection of randomly addressable blocks, e.g., disks

• Character special files: devices accept/output character stream, e.g., printers, modems

• Pipe: pseudofile connecting two processes

A B

PipeProcess Process

58

Outline






• System calls


59

System Calls

• Interface between OS and user programs

• Similar underlying concepts– Details vary from OS to OS

• A procedure library for programming languages– Like making a special procedure call

60

System Call Read

• A call in C: count=read(fd, buffer, nbytes);– Count # of bytes really read– If failed, count -1– errno error number

61

Making System Call read()

Count # of bytes really read

If failed, count -1, errno error number

count=read(fd, buffer, nbytes);

62

POSIX System Calls: Process Management• Fork()

• Waitpid(pid, &statloc, options)

• Execve(name, argv, environp)

• Exit(status)

63

POSIX System Calls: File Management• Open(file, how, …)

• Close(fd)

• Read(fd, buffer, nbytes)

• Write(fd, buffer, nbytes)

• Lseek(fd, offset, whence)

• Stat(name, &buf)

64

POSIX System Calls: Directory and File System Management• Mkdir(name, mode)

• Rmdir(name)

• Link(name1, name2)

• Unlink(name)

• Mount(special, name, flag)

• Umount(special)

65

POSIX System Calls: Miscellaneous• Chdir(dirname)

• Chmod(name, mode)

• Kill(pid, signal)

• Time(&seconds)

66

Win32 API CallsWin32 UNIX Win32 UNIX

CreateProcess fork CreateDirectory mkdir

WaitForSigleObject waitpid RemoveDirectory rmdir

(none) execve (none) link

ExitProcess exit DeleteFile unlink

CreateFile open (none) mount

CloseHandle close (none) umount

ReadFile read SetCurrentDirectory chdir

WriteFile write (none) chmod

SetFilePointer lseek (none) kill

GetFileAttributesEx stat GetLocalTime time

67

Outline






• System calls


68

Monolithic Systems

• No structure as a good structure– OS: a collection of procedures

• Three layers of procedures

Invoke requested service procedure

Carry out system calls

Help service procedures

Main procedures

Service procedures

Utility procedures

69

Relation Among Procedures

• A main program– Involve the requested service procedures

• A set of service procedures– Carry out the system calls

• A set of utility procedures– Help the service procedures

70

Layered SystemsTHE system

MULTICS

professor

students

System calls

Layer Function

5 The operator

4 User programs

3 Input/output management

2 Operator-process communication

1 Memory and drum management

0 Processor allocation and multiprogramming

71

Virtual Machines

• Virtual machine monitor (VM/370)

– Multiprogramming by multiple virtual machines

– Each virtual machine is exact copies of 370

• Operating systems run on virtual machines

– Two level traps

System calls hereI/O incrustations here CMS CMS CMS Trap here

Trap here VM/370

370 bare hardware

72

Exokernels

• Give each user a clone of actual computer, but with a subset of the resources

• Two levels– Exokernel: allocate/maintain resources to virtual

machines– OS: run on virtual machines

• Advantages– Save a layer of mapping– Separate multiprogramming from user OS code

with less overhead

73

Client-server Model

• Move code from kernel up into higher layers

– Kernel minimal microkernel

– Implement most of the OS in user processes

Client process

Client process

Process server

Terminal server

…File

serverMemory server

User mode

MicrokernelKernel mode

Client obtains service by sending messages to server processes

74

Advantages of Client-server Model

• Robust– A bug may cause crash within a module only

• Adaptable– Easy to implement in distributed systems

Machine 1

Client

kernel

Machine 2

File server

kernel

Machine 3

process server

kernel

Machine 4

Terminal server

kernel

NetworkMessage from client to server

75

Summary

• Operating systems = resource managers + extended machines

• Operating systems evolve as hardware evolving• Review of computers hardware for good

understanding of operating systems• Basic concepts of OS: processes, memory

management, I/O management, file system, security

• System calls as heart of operating systems• Structures of operating systems

Chapter 1 Introduction. 2 Outline What is an operating system? History of operating systems...

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