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Transcript of Operating System 24643
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Chapter 2: Operating-System Structures
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2.2 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Chapter 2: Operating-System Structures
Operating System Services User Operating System Interface
System Calls
Types of System Calls
System Programs
Operating System Design and Implementation
Operating System Structure
Virtual Machines
Operating System Generation
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2.3 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
OS Views
Interface Components
services
OS
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2.4 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating System Services
One set of operating-system services provides functions that arehelpful to the user:
User interface - Almost all operating systems have a user interface (UI)
Varies between Command-Line (CLI), Graphics User Interface(GUI), Batch
Program execution - The system must be able to load a program intomemory and to run that program, end execution, either normally orabnormally (indicating error)
I/O operations - A running program may require I/O, which mayinvolve a file or an I/O device.
File-system manipulation - The file system is of particular interest.Obviously, programs need to read and write files and directories, createand delete them, search them, list file Information, permissionmanagement.
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2.5 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating System Services (Cont.)
One set of operating-system services provides functions that arehelpful to the user (Cont):
Communications Processes may exchange information, on the samecomputer or between computers over a network
Communications may be via shared memory or through messagepassing (packets moved by the OS)
Error detection OS needs to be constantly aware of possible errors
May occur in the CPU and memory hardware, in I/O devices, in userprogram
For each type of error, OS should take the appropriate action to
ensure correct and consistent computing Debugging facilities can greatly enhance the users and
programmers abilities to efficiently use the system
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2.6 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating System Services (Cont.)
Another set of OS functions exists for ensuring the efficient operation of thesystem itself via resource sharing
Resource allocation - When multiple users or multiple jobs runningconcurrently, resources must be allocated to each of them
Many types of resources - Some (such as CPU cycles,main memory,and file storage) may have special allocation code, others (such as I/Odevices) may have general request and release code.
Accounting - To keep track of which users use how much and what kindsof computer resources
Protection and security - The owners of information stored in a multiuseror networked computer system may want to control use of that information,concurrent processes should not interfere with each other
Protection involves ensuring that all access to system resources is
controlled Security of the system from outsiders requires user authentication,
extends to defending external I/O devices from invalid access attempts
If a system is to be protected and secure, precautions must beinstituted throughout it.
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User Operating System Interface
CLI, GUI, and Batch
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User Operating System Interface - CLI
CLI allows direct command entry Sometimes implemented in kernel, sometimes by systems
program
Sometimes multiple flavors implementedshells
Primarily fetches a command from user and executes it
Sometimes commands built-in, sometimes just names ofprograms
If the latter, adding new features doesnt require shell
modification
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User Operating System Interface - GUI
User-friendly desktop metaphor interface
Usually mouse, keyboard, and monitor
Icons represent files, programs, actions, etc
Various mouse buttons over objects in the interface causevarious actions (provide information, options, execute function,
open directory (known as a folder) Invented at Xerox PARC
Many systems now include both CLI and GUI interfaces
Microsoft Windows is GUI with CLI command shell
Apple Mac OS X as Aqua GUI interface with UNIX kernel
underneath and shells available
Solaris is CLI with optional GUI interfaces (Java Desktop, KDE)
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System Calls
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System Calls
Programming interface to the services provided by the OS
Typically written in a high-level language (C or C++)
Mostly accessed by programs via a high-level Application ProgramInterface (API) rather than direct system call use
Three most common APIs are Win32 API for Windows, POSIX API forPOSIX-based systems (including virtually all versions of UNIX, Linux, and
Mac OS X), and Java API for the Java virtual machine (JVM) Why use APIs rather than system calls?
Portability
System calls are more detailed and difficult to work with.
(Note that the system-call names used throughout this text are generic)
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Example of System Calls
System call sequence to copy the contents of one file to anotherfile
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Example of Standard API
Consider the ReadFile() function in the
Win32 APIa function for reading from a file
A description of the parameters passed to ReadFile()
HANDLE filethe file to be read
LPVOID buffera buffer where the data will be read into and writtenfrom
DWORD bytesToReadthe number of bytes to be read into the buffer
LPDWORD bytesReadthe number of bytes read during the last read
LPOVERLAPPED ovlindicates if overlapped I/O is being used
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System Calls Implementation
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System Call Implementation
Typically, a number associated with each system call
System-call interface maintains a table indexed according tothese numbers
The system call interface invokes intended system call in OS kerneland returns status of the system call and any return values
The caller need know nothing about how the system call isimplemented
Just needs to obey API and understand what OS will do as aresult call
Most details of OS interface hidden from programmer by API
Managed by run-time support library (set of functions builtinto libraries included with compiler)
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API System Call OS Relationship
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Standard C Library Example
C program invoking printf() library call, which calls write() system call
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System Call Parameter Passing
Often, more information is required than simply identity of desired
system call
Exact type and amount of information vary according to OSand call
Three general methods used to pass parameters to the OS
Simplest: pass the parameters in registers
In some cases, may be more parameters than registers
Parameters stored in a block, or table, in memory, and addressof block passed as a parameter in a register
This approach taken by Linux and Solaris
Parameters placed, or pushed, onto the stackby the program
and poppedoff the stack by the operating system Block and stack methods do not limit the number or length of
parameters being passed
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Parameter Passing via Table
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Types of System Calls
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Types of System Calls
Process control
Load, execute, create process, wait, etc.
Differs between single-tasking and multi-tasking.
File management
Create/delete file, open/close, read/write, etc.
Device management
Read, write, reposition, attach/detach device, etc.
Information maintenance.
Get time/date/process/file, set time/date/process/file, etc.
Communications
Send/receive messages , create/delete communication,etc.
Two models for IPC (interprocess communication):messages-passing and shared-memory.
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System programs
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2.23 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
System Programs
System programs provide a convenient environment forprogram development and execution. They can be dividedinto:
File manipulation
Status information
File modification
Programming language support
Program loading and execution
Communications
Application programs
Most users view of the operation system is defined by
system programs, not the actual system calls
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OS Design and Implementation
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2.25 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
OS structure
Its not always clear how to stitch OS modules together:
MemoryManagement
I/O System
Secondary StorageManagement
File System
Protection System
Accounting System
Process Management
Command Interpreter
Information Services
Error Handling
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2.26 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating System Design and Implementation
Design and Implementation of OS not solvable, but some
approaches have proven successful
Internal structure of different Operating Systems can varywidely
Start by defining goals and specifications
Affected by choice of hardware, type of system
Usergoals and Systemgoals
User goals operating system should be convenient touse, easy to learn, reliable, safe, and fast
System goals operating system should be easy todesign, implement, and maintain, as well as flexible,reliable, error-free, and efficient
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2.27 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating System Design and Implementation (Cont.)
Important principle to separate
Policy: What will be done? E.g timer construct. how longdoes a timer need to be set
Mechanism: How to do it?
Mechanisms determine how to do something, policies
decide what will be done The separation of policy from mechanism is a very
important principle, it allows maximum flexibility if policydecisions are to be changed later
Implementation: usually using a combination of high-level
and low level programming languages (i.e. Assembly,C/C++).
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OS Structure
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2.29 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating Systems Structure(What is the organizational Principle?)
Simple (i.e. monolithic) Only one or two levels of code
Layered
Lower levels independent of upper levels
Microkernel
OS built from many user-level processes
Modular
Core kernel with Dynamically loadable modules
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2.30 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Early structure: Monolithic
Traditionally, OSs (like UNIX, DOS) were built as a monolithicentity:
everything
user programs
hardware
OS
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2.31 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
MS-DOS Layer Structure
MS-DOS written to provide the
most functionality in the leastspace
Not divided into modules
Interfaces and levels offunctionality not wellseparated
S S
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2.32 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
UNIX: Also Simple Structure
UNIX limited by hardware functionality
Original UNIX operating system consists of two separable parts:
Systems programs
The kernel
Consists of everything below the system-call interface andabove the physical hardware
Provides the file system, CPU scheduling, memorymanagement, and other operating-system functions;
Many interacting functions for one level
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2.33 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
UNIX System Structure
User Mode
Kernel Mode
Hardware
Applications
Standard Libs
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2.34 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Monolithic design
Major advantage: cost of module interactions is low (procedure call)
Disadvantages:
hard to understand
hard to modify
unreliable (no isolation between system modules)
hard to maintain
What is the alternative?
find a way to organize the OS in order to simplify its designand implementation
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2.35 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Layered Approach
The operating system is divided into a number oflayers (levels), each built on top of lower layers.The bottom layer (layer 0), is the hardware; thehighest (layer N) is the user interface.
With modularity, layers are selected such thateach uses functions (operations) and services ofonly lower-level layers
Advantage: modularity Easier debugging/Maintenance
Not always possible: Does process scheduler lie above or
below virtual memory layer?
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2.36 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Layered Operating System
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2.37 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Microkernel System Structure
Moves as much from the kernel into user space
Communication takes place between user modules using messagepassing
Benefits:
Easier to extend a microkernel
Easier to port the operating system to new architectures More reliable (less code is running in kernel mode)
More secure
Detriments:
Performance overhead of user space to kernel spacecommunication
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2.38 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Microkernel vs. Monolithic
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2.39 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Modules-based Structure
Most modern operating systems implement kernel modules
Uses object-oriented approach
Each core component is separate
Each talks to the others over known interfaces
Each is loadable as needed within the kernel
Overall, similar to layers but with more flexibility and more efficientthan microkernel
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Virtual Machines
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2.41 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Virtual Machines
A virtual machinetakes the layered approachto its logical conclusion. It treats hardware andthe operating system kernel as though theywere all hardware
A virtual machine provides an interfaceidenticalto the underlying bare hardware
The operating system creates the illusion ofmultiple processes, each executing on its own
processor with its own (virtual) memory
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2.42 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Virtual Machines (Cont.)
The resources of the physical computer areshared to create the virtual machines
CPU scheduling can create the appearancethat users have their own processor
Spooling and a file system can provide virtualcard readers and virtual line printers
A normal user time-sharing terminal serves asthe virtual machine operators console
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2.43 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Virtual Machines Implementation
Virtual-machine software -> kernel mode(VMWare)
Virtual-machine itself -> user mode (Ubuntu)
Inside Virtual-machine itself we have virtual kernel
mode and virtual user mode.
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2.44 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Virtual Machines (Cont.)
(a) Non-virtual machine (b) virtual machine
Non-virtual MachineVirtual Machine
Virt al Machines (b fit )
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2.45 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Virtual Machines (benefits)
The virtual-machine concept provides completeprotection of system resources since each virtualmachine is isolated from all other virtual machines.This isolation, however, permits no direct sharing ofresources.
A virtual-machine system is a perfect vehicle foroperating-systems research and development.System development is done on the virtual machine,instead of on a physical machine and so does not
disrupt normal system operation.
The virtual machine concept is difficult to implementdue to the effort required to provide an exactduplicate to the underlying machine
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2.46 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
VMware Architecture
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2.47 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
The Java Virtual Machine
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2.48 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Operating System Generation
Operating systems are designed to run on any ofa class of machines; the system must beconfigured for each specific computer site
SYSGEN program obtains information concerningthe specific configuration of the hardware system
C
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2.49 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
Conclusion
Rapid Change in Hardware Leads to changing OS
Standard Components and Services
Process Control
Main Memory
I/O
File System
UI
Policy vs Mechanism
Crucial division: not always properly separated!
Complexity is always out of control
R f
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2.50 Silberschatz, Galvin and Gagne 2005Operating System Concepts 7th Edition, Jan 14, 2005
References
Pictures & some slidesProf. Kubiatowicz, Berkeley university,
Prof. Kimura & Zbikowski, WashingtonUniversity
Wikipedia
Content
Text book
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End of Chapter 2