1 Operating Systems (202-1-3031) Lecturers : Danny Hendler and Amnon Meisels TAs: Amir Gershman,Alon...

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Operating Systems (202-1-3031)

LecturersLecturers: : Danny Hendler Danny Hendler and and Amnon MeiselsAmnon MeiselsTATAs: Amir Gershman,s: Amir Gershman, Alon Grubshtein, Amir Mentchel, Alon Grubshtein, Amir Mentchel,

Dolev Pomerantz Dolev Pomerantz

Course siteCourse site: http://www.cs.bgu.ac.il/~os112/Main

Danny HendlerDanny Hendler

Office: Alon, 218Office: Alon, 218 [email protected]@cs.bgu.ac.il Office hours:Office hours:

Wed., 12-14Wed., 12-14

Amnon MeiselsAmnon Meisels

Office: Alon, 206Office: Alon, 206 [email protected]@cs.bgu.ac.il Office hours: Office hours:

Thu. 12-14Thu. 12-14

1Operating Systems, 2011, Danny Hendler & Amnon Meisels

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Assignments and grade structureAssignments and grade structure

AssignmentSubjectWeightProgramming 1 + 2Scheduling +

Synchronization 15%

Programming 3 + 4Memory Management + Files

15%

MidtermProcesses, scheduling, synchronization,memory

15%

FinalAll55%

Assignments and exams are mandatory Must pass final exam

2Operating Systems, 2011, Danny Hendler & Amnon Meisels

TextbooksTextbooks A. Tanenbaum: Modern Operating Systems, Prentice-Hall, 3rd

Edition, 2008

A. Silbetschatz et al.: Operating System Concepts (8th ed.), Addison Wesley, 2009

G. Nutt: Operating Systems (a modern perspective) (3rd ed.), Addison Wesley, 2003

W. Stallings: Operating Systems (6th ed.), Prentice-Hall, 2009

Operating Systems, 2011, Danny Hendler & Amnon Meisels 3

SyllabusSyllabus1. Introduction - History; Views; Concepts; Structure2. Process Management - Processes; State + Resources; Threads;

Unix implementation of Processes3. Scheduling – Paradigms; Unix; Modeling4. Synchronization - Synchronization primitives and their

equivalence; Deadlocks5. Memory Management - Virtual memory; Page replacement

algorithms; Segmentation 6. File Systems - Implementation; Directory and space

management; Unix file system; Distributed file systems (NFS)7. Security – General policies and mechanisms; protection models;

authentication8. Multiprocessors (if there’s time)


Introduction: outlineIntroduction: outline

What is an operating system?

Some history

OS concepts

OS structure


Layered Hardware-Software Layered Hardware-Software Machine ModelMachine Model

Operating System

Compilers Editors ShellSystemPrograms

Banking System Airline reservation Web browserApplications

Hardware


Computer-System ArchitectureComputer-System Architecture


What is an Operating System ?What is an Operating System ?

An operating system is:

1. An Extended Machine

2. A Resource manager


Operating Systems as extended MachinesOperating Systems as extended Machines

The problems:Bare machine has complex structure

o Processorso Many difficult-to-program devices

Primitive Instruction SetDifferent for Different Machines

OS provides: Abstraction!

– Simple, easier to use interface (machine-independent)– Hiding of unnecessary details


OS abstraction example: read from diskOS abstraction example: read from disk

Read file data from disk (simplified)… Read linear sector 17,403 from disk 2 Convert linear sector number to: cylinder, sector, head

(may be complicated – outer cylinders have more sectors, bad sectors remapped, etc.)

Move disk arm to requested cylinder Wait for proper sector to appear

…

OS abstractionreturn-code = read(fd, buff, nbytes)


UNIX high-level architectureUNIX high-level architecture

UserInterface


Operating Systems as Resource ManagersOperating Systems as Resource Managers Multiple resources

o Processors; Memoryo Disks; Tapes; Printerso Network interfaces; Terminals

Controlled allocation of Resources among:o Groups, Users; Processes, Threads,…

Means of control: sharing/multiplexing/scheduling, monitoring, protection, report/payment




Some history

OS concepts

OS structure


Operating Systems, 2011, Danny Hendler & Amnon Meisels

History of Operating SystemsHistory of Operating Systems First generation 1945 - 1955

o vacuum tubes, plug boards – user plugs-in programuser plugs-in program

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http://www.tietokonemuseo.saunalahti.fi/eng/kuva_51_eng.htm


The first computersThe first computers

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Electronic Numerical Integrator And Computer (ENIAC)

Mathematical Analyzer, Numeric Integrator And Computer(MANIAC)


Second generation 1955 - 1965o transistors, batch systems – multiple programs on multiple programs on DiskDisk

Third generation 1965 – 1980o ICs and multiprogramming - user interaction (user interaction (time-sharingtime-sharing))

Fourth generation 1980 – presento personal computers – graphic user-interfacegraphic user-interfaceo Networks – file & computing file & computing servicesserviceso Web-computing, Handheld devices , Cellular phones, …Handheld devices , Cellular phones, …

History of Operating Systems History of Operating Systems (cont’d)(cont’d)

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How Bill Gates became rich…How Bill Gates became rich…

1974: Intel releases the 8080 processor, needs an OS

Gary Kildall

Please! develop an OS

CP/M OS

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http://www.itnews.sk/buxus_dev/images/2006/Intel_logo_nove1_velky.jpg

How Bill Gates became rich…How Bill Gates became rich…(cont’d)(cont’d)

1974: Intel releases the 8080 processor, needs an OS

Gary Kildall

CP/M OS

Can you grant me CP/M rights?

Sure!



1980: IBM designs IMB PC, needs an OS

Gary Kildall

Can you find an OS for our PC?

Please meet IBM, they need an OS

Sorry, too busy!!!!!




Kildall too busy. Please develop an

OS!

I’de like to buy the DOS OS

Sure, it’s yours for $75,000




May I retain the rights for MS-

DOS?

Sure, why not!!



Well, this is 20:20 hind vision…




Some history

OS concepts

OS structure


OS – Key FunctionsOS – Key Functions Process management

o process creation; deletion; suspension/preemptiono process synchronization; communication; scheduling

Main-memory managemento Manage used parts and their current userso Select processes to load from secondary storageo Allocate memory to running processes

Secondary storage managemento Free-space managemento Storage allocation


File system managemento File + directory - creation; deletiono File manipulation primitiveso Mapping files onto secondary storage

I/O system managemento general device-driver interfaceo Drivers for specific hardware devices

Protection systemo Distinguish between authorized and unauthorized usageo Provide means of enforcement

OS – Key Functions OS – Key Functions (cont’d)(cont’d)


Processes - a key conceptProcesses - a key concept

Resource container for “program in execution” Timesharing, process suspension/preemption Process Table Process Groups Signals


Why do we need multiple processes?Why do we need multiple processes?

• Single application: We want things to happen “concurrently” (E.g.: paging and typing in a text editor)

• Multiple applications: processes running in the background (e.g., Anti Virus)

• Multiple users: The departmental computer; all types of Servers


CPU much faster than I/Oo Computation/communication overlap

Memory large enough – requires memory protection! Scheduler which manages flow of jobs in and out

and shares CPU between jobs – requires Timer Spooler which takes care of very slow I/O devices

(e.g., printer spooler). simultaneous peripheral operations on-line...

MultiprogrammingMultiprogramming: how is it done?: how is it done?


Process treesProcess trees

• A process tree A created two child processes, B and C B created three child processes, D, E, and F


Inter-Process Communication (IPC)Inter-Process Communication (IPC)

Two processes communicating via a pipe


Files: non volatile dataFiles: non volatile data

File types and operations on filesDirectories - hierarchical structureWorking directories

Root directory

Students

Gil

Roni

Or

Faculty

Amnon

Papers Progs Grants


Protection and SecurityUnix - user; group; other (rwx bits)

File descriptors (handles) I/O as a special file Block & Character special files Standard input; output; error Pipes Links

Files: non volatile data Files: non volatile data (cont’d)(cont’d)


I/O is performed in kernel modeI/O is performed in kernel mode

All I/O instructions are privileged instructionsprivileged instructions I/O devices and CPU can execute concurrently CPU moves data between main memory and device

controllers' buffers (done by device drivers) Device controllers interruptinterrupt upon completion Interrupts or Traps enable mode switching

Operating systems are interrupt-driveninterrupt-driven Traps/signalsTraps/signals: software interrupts: software interrupts


Interrupts and the Interrupts and the fetch-decode-execute loopfetch-decode-execute loop

While (halt flag not set during execution){IR = memory[PC];execute(IR);PC++;If(Interrupt_Request) {

memory[0] = PC;PC = memory[1] }

} An interrupt is an asynchronous event The kernel interrupt handling routine may use a

disable_interrupts instruction to avoid losing data while processing an interrupt request

Interrupt handler is typically called indirectly via the interrupt vector

Simplist

ic!


Synchronous vs. Asynchronous I/O Synchronous vs. Asynchronous I/O

execute


Steps in Making a System Call Steps in Making a System Call

There are 11 steps in making the system call: read (fd, buffer, nbytes)

Is this call Synchronous or Asynchronous?


System CallsSystem Calls

processes

files

directories

miscellaneous


The Shell Command LanguageThe Shell Command Language

sort < file1 > file2sort < file1 > file2 cat file1 | sort | lprcat file1 | sort | lpr

• The Shell is a process which executes its commands as offspringoffspring processesprocesses

• Processes may call shell commands by using the “system” system call


Shell structure – Parent & childShell structure – Parent & childA stripped-down shell:

while (TRUE) { /* repeat forever */ type_prompt( ); /* display prompt */ read_command (command, parameters)/* input from terminal */ if (fork() > 0) { /* fork off child process */ /* Parent code */ wait(); /* wait for child to exit */ } else { /* Child code */ execvp (command, parameters); /* execute command */ }}


Shell initializationShell initialization

The init program runs getty on all ports Upon detecting a terminal, getty runs login Typing in a user name and a password – login

checks the passwdpasswd file and if correct runs a shell – the one specified in the UID entry

The shell is run with that user ID environment parameters


Running user commandsRunning user commands User types: ‘grep some_word file_name’ Shell parses the command, inserts the strings grep, some_word,

file_name into argv and their number to argc Next, the shell uses fork() to create a process (same user ID) Now, it takes the executable name grep and the arguments, all

from argv, and uses execvp() (or a similar system call) to run the grep executable

On foreground execution, the shell would use the wait() system call and continue its session only after the child process terminates



UNIX Utility Programs

A few of the more common UNIX utility programs required by POSIX

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Some history

OS concepts

OS structure


Operating system structureOperating system structure

1. Monolithic systems

2. Virtual machines

3. Client-server model

…


Monolithic systems Monolithic systems

Monolithic systems have little structure

ServiceRoutines

Utilityprocedures

Main procedure forinvoking OS service


Monolithic systems Monolithic systems

Service routines are system callsUtility procedures serve multiple

service routinesAll compiled into a single system


Virtual MachinesVirtual Machines Provide an interface identicalidentical to the underlying bare machinebare machine VM monitor creates multiple VMs, each executing on its own

(virtual) processor and its own (virtual) memory Virtual machines provide complete protection of system

resources - even separate resourcesseparate resources Difficult to implement, due to the effort required to provide an

exactexact duplicate of the underlying machine Well-known examples:

o MS-DOS on top of Windowso JVM


Virtual Machines: IBM 370Virtual Machines: IBM 370

370 bare hardware

VM/370

CMS CMS CMSkernel

user

CMS: Conversational Monitor System, a single user OS


Virtual Machines Virtual Machines (cont’d)(cont’d)


Modern virtual machinesModern virtual machines

Different legacy servers run on different OSHost sharing Host sharing for web serversUse two different OS on same machineA privileged instruction executed in user mode

does not trap automatically does not trap automatically (ignored)Type II VM – run a host operating systemhost operating systemIncidentally, provides very good securitysecurity


MicrokernelsMicrokernels

Small number of lines of code mostly in CCatching interrupts and switching processes in

AssemblyC code manages and schedules processes,

inter-process communication, i/o interaction Offers few (~40) system calls for the rest of OS Device drivers (Disk, Network,…) in user mode Upper level contains Servers – File, Process..


Client-Server ModelClient-Server Model

(Micro)Kernel

Client Process

Client Process

. . . . . . FileServer

MemoryServer

Client File Server Process Server

Kernel Kernel Kernel Kernel

Machine1 Machine2 Machine3 Machine4

. . . . . . .

Network Distributed System


Client/server architecture:Client/server architecture:Mechanism vs. PolicyMechanism vs. Policy

Simple Kernel - modularity; minimal “privileged” operation

Servers for files, memory, etc. - distribution; user mode operation

good for distributed systems

Mechanism in kernel - howhow to do things..

Policy outside - decide whatwhat to do; can be changed later..changed later.. Critical servers in kernel – i/o disk server & the Scheduler – who i/o disk server & the Scheduler – who

serves who….serves who….


1 Operating Systems (202-1-3031) Lecturers : Danny Hendler and Amnon Meisels TAs: Amir Gershman,Alon...

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