Transcript Operating Systems, 082

Operating Systems (202-1-3031)
Danny Hendler
Amnon Meisels
 Office: Alon, 218
 [email protected]
 Office hours:
Wed., 11-13
 Office:
 [email protected]
 Office hours:
Lecturers: Danny Hendler and Roie Zivan
TAs: Alon Grubshtein, Amir Mentchel, Ilya Misrky and
Dolev Pomerantz
Course site: http://www.cs.bgu.ac.il/~os122/Main
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Assignments and grade structure
Assignment
Subject
Weight
Programming 1 + 2 Scheduling +
Synchronization
Programming 3 + 4 Memory Management
+ Files
15%
Midterm
15%
Final
Processes, scheduling,
synchronization,
memory (TBD)
All
15%
55%
 Assignments and exams are mandatory
 Must pass final exam
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Textbooks
 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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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. Security – General policies and mechanisms; protection models;
authentication
8. Distributed Synchronization (if there's time)
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Introduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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Layered Hardware-Software
Machine Model
Applications
System
Programs
Banking System Airline reservation
Compilers
Editors
Web browser
Shell
Operating System
Hardware
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Computer-System Architecture
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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 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
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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)
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UNIX high-level architecture
User
Interface
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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
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Introduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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History of Operating Systems
 First generation 1945 - 1955
o vacuum tubes, plug boards – user plugs-in program
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The first computers
Electronic Numerical Integrator And Computer (ENIAC)
Mathematical Analyzer, Numeric Integrator And Computer(MANIAC)
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History of Operating Systems (cont’d)
 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…
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How Bill Gates became rich…
1974: Intel releases the 8080 processor, needs an OS
Please! develop
an OS
CP/M OS
Gary Kildall
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How Bill Gates became rich…(cont’d)
1974: Intel releases the 8080 processor, needs an OS
CP/M OS
Sure!
Can you grant me
CP/M rights?
Gary Kildall
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How Bill Gates became rich…(cont’d)
1980: IBM designs IMB PC, needs an OS
Can you find an
OS for our PC?
Please meet IBM, they need an OS
Gary Kildall
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How Bill Gates became rich…(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…(cont’d)
1980: IBM designs IMB PC, needs an OS
May I retain the
rights for MSDOS?
Sure, why not!!
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How Bill Gates became rich…(cont’d)
Well, this is 20:20 hind vision…
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Introduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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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
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OS – Key Functions (cont’d)
 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
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Processes - 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?
• 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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Multiprogramming: how is it done?
 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
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Process 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)
Two processes communicating via a pipe
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Files: non volatile data
File types and operations on files
Directories - hierarchical structure
Working directories
Root di re ctory
S tu de n ts
Facu l ty
Am n on
Gi l
Or
Ron i
Pape rs
Progs
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Files: non volatile data (cont’d)
 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
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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
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Interrupts and the
fetch-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
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Synchronous vs. Asynchronous I/O
execute
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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 Calls
processes
files
directories
miscellaneous
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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
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Shell structure – Parent & child
A stripped-down shell:
while (TRUE) {
type_prompt( );
read_command (command, parameters)
if (fork() > 0) {
/* Parent code */
wait();
} else {
/* Child code */
execvp (command, parameters);
}
/* repeat forever */
/* display prompt */
/* input from terminal */
/* fork off child process */
/* wait for child to exit */
/* execute command */
}
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Shell 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 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
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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
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UNIX Utility Programs
A few of the more common UNIX utility programs required by POSIX
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Introduction: outline
What is an operating system?
Some history
OS concepts
OS structure
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Operating system structure
1. Monolithic systems
2. Virtual machines
3. Client-server model
…
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Monolithic systems
Monolithic systems have little structure
Main procedure for
invoking OS service
Service
Routines
Utility
procedures
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Monolithic systems
Service routines are system calls
Utility procedures serve multiple service routines
All compiled into a single system
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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
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Virtual Machines: IBM 370
user
CMS
CMS
CMS
kernel
VM/370
370 bare hardware
CMS: Conversational Monitor System, a single user OS
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Virtual Machines (cont’d)
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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
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Microkernels
Small number of lines of code mostly in C
Catching interrupts and switching processes in
Assembly
C code manages and schedules processes, interprocess 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 Model
Client
Process
Client
Process
......
File
Server
Memory
Server
(Micro)Kernel
Machine1
Machine2
Client
File Server
Kernel
Kernel
....
Network
Machine4
Machine3
Process Server
Kernel
Kernel
...
Distributed System
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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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