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Operating Systems (202-1-3031)
LecturersLecturers: : Danny Hendler Danny Hendler and and Roie ZivanRoie ZivanTATAs: Alon Grubshtein, Amir Mentchel, Ilya Misrky ands: Alon Grubshtein, Amir Mentchel, Ilya Misrky and
Dolev Pomerantz Dolev Pomerantz
Course siteCourse site: http://www.cs.bgu.ac.il/~os122/Main
Danny HendlerDanny Hendler
Office: Alon, 218Office: Alon, 218 [email protected]@cs.bgu.ac.il Office hours:Office hours:
Wed., 11-13Wed., 11-13
Amnon MeiselsAmnon Meisels
Office:Office: [email protected]@gmail.com Office hours: Office hours:
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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 (TBD)
15%
FinalAll55%
Assignments and exams are mandatory Must pass final exam
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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
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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. Distributed Synchronization (if there's time)
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Introduction: outlineIntroduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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Layered Hardware-Software Layered Hardware-Software Machine ModelMachine Model
Operating System
Compilers Editors ShellSystemPrograms
Banking System Airline reservation Web browserApplications
Hardware
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Computer-System ArchitectureComputer-System Architecture
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What is an Operating System ?What is an Operating System ?
An operating system is:
1. An Extended Machine
2. A Resource manager
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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
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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)
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UNIX high-level architectureUNIX high-level architecture
UserInterface
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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
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Introduction: outlineIntroduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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Operating Systems, 2012, Danny Hendler & Roie Zivan
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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The first computersThe first computers
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Electronic Numerical Integrator And Computer (ENIAC)
Mathematical Analyzer, Numeric Integrator And Computer(MANIAC)
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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, Cloud computing…Handheld devices , Cellular phones, Cloud computing…
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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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!
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How Bill Gates became rich…How Bill Gates became rich…(cont’d)(cont’d)
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!!!!!
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How Bill Gates became rich…How Bill Gates became rich…(cont’d)(cont’d)
1980: IBM designs IMB PC, needs an OS
Kildall too busy. Please develop an
OS!
I’de like to buy the DOS OS
Sure, it’s yours for $75,000
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How Bill Gates became rich…How Bill Gates became rich…(cont’d)(cont’d)
1980: IBM designs IMB PC, needs an OS
May I retain the rights for MS-
DOS?
Sure, why not!!
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How Bill Gates became rich…How Bill Gates became rich…(cont’d)(cont’d)
Well, this is 20:20 hind vision…
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Introduction: outlineIntroduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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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
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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)
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Processes - a key conceptProcesses - a key concept
Resource container for “program in execution” Timesharing, process suspension/preemption Process Table Process Groups Signals
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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
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CPU much faster than I/Oo Computation/communication overlap
Memory large enough – requires memory protection!
Scheduler which manages flow of jobs in and outand shares CPU between jobs – requires Timer
MultiprogrammingMultiprogramming: how is it done?: how is it done?
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Process treesProcess trees
• A process tree A created two child processes, B and C B created three child processes, D, E, and F
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Inter-Process Communication (IPC)Inter-Process Communication (IPC)
Two processes communicating via a pipe
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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
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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)
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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
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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!
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Synchronous vs. Asynchronous I/O Synchronous vs. Asynchronous I/O
execute
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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?
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System CallsSystem Calls
processes
files
directories
miscellaneous
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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
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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 */ }}
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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
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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
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Operating Systems, 2012, Danny Hendler & Roie Zivan
UNIX Utility Programs
A few of the more common UNIX utility programs required by POSIX
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Introduction: outlineIntroduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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Operating system structureOperating system structure
1. Monolithic systems
2. Virtual machines
3. Client-server model
…
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Monolithic systems Monolithic systems
Monolithic systems have little structure
ServiceRoutines
Utilityprocedures
Main procedure forinvoking OS service
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Monolithic systems Monolithic systems
Service routines are system calls
Utility procedures serve multiple service routines
All compiled into a single system
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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 JVMo VMWare
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Virtual Machines: IBM 370Virtual Machines: IBM 370
370 bare hardware
VM/370
CMS CMS CMSkernel
user
CMS: Conversational Monitor System, a single user OS
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Virtual Machines Virtual Machines (cont’d)(cont’d)
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Modern virtual machinesModern virtual machines
Different legacy servers run on different OS
Host sharing Host sharing for web servers
Use multiple operating systems on a single machine
Security through isolation
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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..
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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
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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….
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