Operating Systems (202-1-3031) - BGUos152/wiki.files/Introduction.pdfOperating Systems, 2015, Meni...

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Operating Systems (202-1-3031)

Lecturers: Meni Adler, Danny Hendler and Roie Zivan

TAs: Dan Brownstein, Zohar Komarovsky, Matan Drory, Omer Litov, Vadim Levit

Course site: http://www.cs.bgu.ac.il/~os152/Main

Meni Adler Office: Alon, 109

[email protected] Office hours:

Tuesdays, 08:00-10:00

Danny Hendler Office: Alon, 218


Tuesdays, 11:00-13:00

Roie Zivan Office: 16 build., 261


Sundays, 09:00-11:00

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Assignments and grade structure

Weight Subject Assignment

15% Scheduling + Synchronization

Programming 1 + 2

15% Memory Management + Files

Programming 3 + 4

15% Processes, scheduling, synchronization, memory (TBD)

Midterm

55% All Final

Assignments and exams are mandatory

Must pass final exam

Textbooks

A. Tanenbaum: Modern Operating Systems, Prentice-Hall, 3rd Edition, 2008

A. Silbetschatz et al.: Operating System Concepts (9th ed.), Addison Wesley, 2012

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

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

Operating Systems, 2015, Meni Adler, Danny Hendler & Roie Zivan 3

Syllabus 1. Introduction - History; Views; Concepts; Structure 2. Process Management - Processes; State + Resources; Threads;

Unix implementation of Processes 3. Scheduling – Paradigms; Unix; Modeling 4. Synchronization - Synchronization primitives and their

equivalence; Deadlocks 5. Memory Management - Virtual memory; Page replacement

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

Unix file system; Distributed file systems (NFS) 7. Distributed Synchronization (if there's time)


Introduction: outline

What is an operating system?

Some history

OS concepts

OS structure


Layered Hardware-Software Machine Model


Computer-System Architecture


What is an Operating System ?

An operating system is:

1. An Extended Machine

2. A Resource manager


Operating Systems as extended Machines

The problems:

Bare machine has complex structure o Processors

o Many difficult-to-program devices

Primitive Instruction Set

Different for Different Machines

OS provides:

Abstraction!

– Simple, easier to use interface (machine-independent)

– Hiding of unnecessary details


OS 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 abstraction return-code = read(fd, buff, nbytes)


UNIX high-level architecture

User Interface


Operating Systems as Resource Managers

Multiple resources o Processors; Memory

o Disks; Tapes; Printers

o 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, 2015, Meni Adler, Danny Hendler & Roie Zivan

History of Operating Systems First generation 1945 - 1955

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

14

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


The first computers

15

Electronic Numerical Integrator And Computer (ENIAC)

Mathematical Analyzer, Numeric Integrator And Computer(MANIAC)


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

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

Fourth generation 1980 – present o personal computers – graphic user-interface

o Networks – file & computing services

o Web-computing, Handheld devices , Cellular phones, Cloud computing…

History of Operating Systems (cont’d)

16


How Bill Gates became rich…

1974: Intel releases the 8080 processor, needs an OS

Gary Kildall

Please! develop an OS

CP/M OS

17

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

How Bill Gates became rich…(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


http://www.digitalresearch.biz/

http://cs.bc.edu/files/IBMlogo.jpg



Kildall too busy. Please develop an

OS!

I’de like to buy the DOS OS

Sure, it’s yours for $75,000



http://upload.wikimedia.org/wikipedia/en/1/1a/RodBrockCard.JPG



May I retain the rights for MS-

DOS?

Sure, why not!!




Well, this is 20:20 hind vision…



http://www.digitalresearch.biz/


http://upload.wikimedia.org/wikipedia/en/1/1a/RodBrockCard.JPG



Some history

OS concepts

OS structure


OS – Key Functions Process management

o process creation; deletion; suspension/preemption

o process synchronization; communication; scheduling

Main-memory management

o Manage used parts and their current users

o Select processes to load from secondary storage

o Allocate memory to running processes

Secondary storage management

o Free-space management

o Storage allocation


File system management o File + directory - creation; deletion

o File manipulation primitives

o Mapping files onto secondary storage

I/O system management o General device-driver interface

o Drivers for specific hardware devices

Protection system o Distinguish between authorized and unauthorized usage

o Provide means of enforcement

OS – Key Functions (cont’d)


Processes - a key concept

Resource container for “program in execution”

Timesharing, process suspension/preemption

Process Table

Process Groups

Signals


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/O

o 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

Multiprogramming: how is it done?


Process 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)

Two processes communicating via a pipe


Files: non volatile data

File types and operations on files

Directories - hierarchical structure

Working directories Root directory

Students

Gil

Roni

Or

Faculty

Amnon

Papers Progs Grants


Protection and Security Unix - 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 (cont’d)


I/O is performed in kernel mode

All I/O instructions are privileged 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 interrupt upon completion

Interrupts or Traps enable mode switching

Operating systems are interrupt-driven

Traps/signals: software interrupts


Interrupts and the fetch-decode-execute loop

Do forever{ 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


Synchronous vs. Asynchronous I/O

execute


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 Calls

processes

files

directories

miscellaneous


The Shell Command Language

sort < file1 > file2

cat file1 | sort | lpr

• The Shell is a process which executes its commands as offspring processes

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


Shell structure – Parent & child

A 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 */

}

}


Linux Shell initialization The init program (process 1) runs getty on all ports

Upon detecting a terminal, getty runs login

Typing in a user name and a password – login checks the passwd 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 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 (חומר העשרה)


Operating system structure

1. Monolithic systems

2. Virtual machines

3. Client-server model

…


Monolithic systems

Monolithic systems have little structure

Service Routines

Utility procedures

Main procedure for invoking OS service


Monolithic systems

Service routines are system calls

Utility procedures serve multiple service routines

All compiled into a single system


Virtual Machines

Provide an interface identical to the underlying bare 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 resources

Difficult to implement, due to the effort required to provide an exact duplicate of the underlying machine

Well-known examples: o MS-DOS on top of Windows

o JVM

o VMWare


Virtual Machines: IBM 370

370 bare hardware

VM/370

CMS CMS CMS kernel

user

CMS: Conversational Monitor System, a single user OS


Virtual Machines (cont’d)


Modern virtual machines

Different legacy servers run on different OS

Host sharing for web servers

Use multiple operating systems on a single machine

Security through isolation


Microkernels

Small number of lines of code mostly in C

Catching interrupts and switching processes in Assembly

C 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 Model

(Micro)Kernel

Client Process

Client Process

. . . . . . File Server

Memory Server

Client File Server Process Server

Kernel Kernel Kernel Kernel

Machine1 Machine2 Machine3 Machine4

. . . . . . .

Network Distributed System


Client/server architecture: Mechanism vs. Policy

Simple Kernel - modularity; minimal “privileged” operation

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

operation

good for distributed systems

Mechanism in kernel - how to do things..

Policy outside - decide what to do; can be changed later..

Critical servers in kernel – i/o disk server & the Scheduler – who serves who….


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