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Silberschatz, Galvin and Gagne ©20023.1
Chapter 3: Operating-System
Structures
System Components
Operating System Services
System Calls
System Programs
System Structure
Virtual Machines
System Design and Implementation
System Generation
Silberschatz, Galvin and Gagne ©20023.2
Common System Components
Process Management
Main Memory Management
File Management
I/O System Management
Secondary Management
Networking
Protection System
Command-Interpreter System
Silberschatz, Galvin and Gagne ©20023.3
Process Management
A process is a program in execution. A process needs
certain resources, including CPU time, memory, files, and
I/O devices, to accomplish its task.
The operating system is responsible for the following
activities in connection with process management.
Process creation and deletion.
process suspension and resumption.
Provision of mechanisms for:
process synchronization
process communication
Silberschatz, Galvin and Gagne ©20023.4
Main-Memory Management
Memory is a large array of words or bytes, each with its
own address. It is a repository of quickly accessible data
shared by the CPU and I/O devices.
Main memory is a volatile storage device. It loses its
contents in the case of system failure.
The operating system is responsible for the following
activities in connections with memory management:
Keep track of which parts of memory are currently being
used and by whom.
Decide which processes to load when memory space
becomes available.
Allocate and deallocate memory space as needed.
Silberschatz, Galvin and Gagne ©20023.5
File Management
A file is a collection of related information defined by its
creator. Commonly, files represent programs (both
source and object forms) and data.
The operating system is responsible for the following
activities in connections with file management:
File creation and deletion.
Directory creation and deletion.
Support of primitives for manipulating files and directories.
Mapping files onto secondary storage.
File backup on stable (nonvolatile) storage media.
Silberschatz, Galvin and Gagne ©20023.6
I/O System Management
The I/O system consists of:
A buffer-caching system
A general device-driver interface
Drivers for specific hardware devices
Silberschatz, Galvin and Gagne ©20023.7
Secondary-Storage Management
Since main memory (primary storage) is volatile and too
small to accommodate all data and programs
permanently, the computer system must provide
secondary storage to back up main memory.
Most modern computer systems use disks as the
principle on-line storage medium, for both programs and
data.
The operating system is responsible for the following
activities in connection with disk management:
Free space management
Storage allocation
Disk scheduling
Silberschatz, Galvin and Gagne ©20023.8
Networking (Distributed Systems)
A distributed system is a collection processors that do not
share memory or a clock. Each processor has its own
local memory.
The processors in the system are connected through a
communication network.
Communication takes place using a protocol.
A distributed system provides user access to various
system resources.
Access to a shared resource allows:
Computation speed-up
Increased data availability
Enhanced reliability
Silberschatz, Galvin and Gagne ©20023.9
Protection System
Protection refers to a mechanism for controlling access
by programs, processes, or users to both system and
user resources.
The protection mechanism must:
distinguish between authorized and unauthorized usage.
specify the controls to be imposed.
provide a means of enforcement.
Silberschatz, Galvin and Gagne ©20023.10
Command-Interpreter System
Many commands are given to the operating system by
control statements which deal with:
process creation and management
I/O handling
secondary-storage management
main-memory management
file-system access
protection
networking
Silberschatz, Galvin and Gagne ©20023.11
Command-Interpreter System
(Cont.)
The program that reads and interprets control statements
is called variously:
command-line interpreter
shell (in UNIX)
Its function is to get and execute the next command
statement.
Silberschatz, Galvin and Gagne ©20023.12
Operating System Services
Program execution – system capability to load a program into
memory and to run it.
I/O operations – since user programs cannot execute I/O
operations directly, the operating system must provide some
means to perform I/O.
File-system manipulation – program capability to read, write,
create, and delete files.
Communications – exchange of information between processes
executing either on the same computer or on different systems
tied together by a network. Implemented via shared memory or
message passing.
Error detection – ensure correct computing by detecting errors
in the CPU and memory hardware, in I/O devices, or in user
programs.
Silberschatz, Galvin and Gagne ©20023.13
Additional Operating System Functions
Additional functions exist not for helping the user, but rather
for ensuring efficient system operations.
• Resource allocation – allocating resources to multiple users
or multiple jobs running at the same time.
• Accounting – keep track of and record which users use how
much and what kinds of computer resources for account
billing or for accumulating usage statistics.
• Protection – ensuring that all access to system resources is
controlled.
Silberschatz, Galvin and Gagne ©20023.14
System Calls
System calls provide the interface between a running
program and the operating system.
Generally available as assembly-language instructions.
Languages defined to replace assembly language for
systems programming allow system calls to be made
directly (e.g., C, C++)
Three general methods are used to pass parameters
between a running program and the operating system.
Pass parameters in registers.
Store the parameters in a table in memory, and the table
address is passed as a parameter in a register.
Push (store) the parameters onto the stack by the program,
and pop off the stack by operating system.
Silberschatz, Galvin and Gagne ©20023.15
Passing of Parameters As A
Table
Silberschatz, Galvin and Gagne ©20023.16
Types of System Calls
Process control
File management
Device management
Information maintenance
Communications
Silberschatz, Galvin and Gagne ©20023.17
MS-DOS Execution
At System Start-up Running a Program
Silberschatz, Galvin and Gagne ©20023.18
UNIX Running Multiple Programs
Silberschatz, Galvin and Gagne ©20023.19
Communication Models
Msg Passing Shared Memory
Communication may take place using either message
passing or shared memory.
Silberschatz, Galvin and Gagne ©20023.20
System Programs
System programs provide a convenient environment for
program development and execution. The can be divided
into:
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.
Silberschatz, Galvin and Gagne ©20023.21
MS-DOS System Structure
MS-DOS – written to provide the most functionality in the
least space
not divided into modules
Although MS-DOS has some structure, its interfaces and
levels of functionality are not well separated
Silberschatz, Galvin and Gagne ©20023.22
MS-DOS Layer Structure
Silberschatz, Galvin and Gagne ©20023.23
UNIX System Structure
UNIX – limited by hardware functionality, the original
UNIX operating system had limited structuring. The UNIX
OS consists of two separable parts.
Systems programs
The kernel
Consists of everything below the system-call interface
and above the physical hardware
Provides the file system, CPU scheduling, memory
management, and other operating-system functions; a
large number of functions for one level.
Silberschatz, Galvin and Gagne ©20023.24
UNIX System Structure
Silberschatz, Galvin and Gagne ©20023.25
Layered Approach
The operating system is divided into a number of layers
(levels), each built on top of lower layers. The bottom
layer (layer 0), is the hardware; the highest (layer N) is
the user interface.
With modularity, layers are selected such that each uses
functions (operations) and services of only lower-level
layers.
Silberschatz, Galvin and Gagne ©20023.26
An Operating System Layer
Silberschatz, Galvin and Gagne ©20023.27
OS/2 Layer Structure
Silberschatz, Galvin and Gagne ©20023.28
Microkernel System Structure
Moves as much from the kernel into “user” space.
Communication takes place between user modules using
message passing.
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
Silberschatz, Galvin and Gagne ©20023.29
Windows NT Client-Server
Structure
Silberschatz, Galvin and Gagne ©20023.30
Virtual Machines
A virtual machine takes the layered approach to its logical
conclusion. It treats hardware and the operating system
kernel as though they were all hardware.
A virtual machine provides an interface identical to the
underlying bare hardware.
The operating system creates the illusion of multiple
processes, each executing on its own processor with its
own (virtual) memory.
Silberschatz, Galvin and Gagne ©20023.31
Virtual Machines (Cont.)
The resources of the physical computer are shared to
create the virtual machines.
CPU scheduling can create the appearance that users have
their own processor.
Spooling and a file system can provide virtual card readers
and virtual line printers.
A normal user time-sharing terminal serves as the virtual
machine operator’s console.
Silberschatz, Galvin and Gagne ©20023.32
System Models
Non-virtual Machine Virtual Machine
Silberschatz, Galvin and Gagne ©20023.33
Advantages/Disadvantages of Virtual Machine
The virtual-machine concept provides complete
protection of system resources since each virtual
machine is isolated from all other virtual machines. This
isolation, however, permits no direct sharing of resources.
A virtual-machine system is a perfect vehicle for
operating-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 implement due
to the effort required to provide an exact duplicate to the
underlying machine.
Silberschatz, Galvin and Gagne ©20023.34
Java Virtual Machine
Compiled Java programs are platform-neutral bytecodes
executed by a Java Virtual Machine (JVM).
JVM consists of
- class loader
- class verifier
- runtime interpreter
Just-In-Time (JIT) compilers increase performance
Silberschatz, Galvin and Gagne ©20023.35
Java Virtual Machine
Silberschatz, Galvin and Gagne ©20023.36
System Design Goals
User goals – operating system should be convenient to
use, easy to learn, reliable, safe, and fast.
System goals – operating system should be easy to
design, implement, and maintain, as well as flexible,
reliable, error-free, and efficient.
Silberschatz, Galvin and Gagne ©20023.37
Mechanisms and Policies
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 policy
decisions are to be changed later.
Silberschatz, Galvin and Gagne ©20023.38
System Implementation
Traditionally written in assembly language, operating
systems can now be written in higher-level languages.
Code written in a high-level language:
can be written faster.
is more compact.
is easier to understand and debug.
An operating system is far easier to port (move to some
other hardware) if it is written in a high-level language.
Silberschatz, Galvin and Gagne ©20023.39
System Generation (SYSGEN)
Operating systems are designed to run on any of a class
of machines; the system must be configured for each
specific computer site.
SYSGEN program obtains information concerning the
specific configuration of the hardware system.
Booting – starting a computer by loading the kernel.
Bootstrap program – code stored in ROM that is able to
locate the kernel, load it into memory, and start its
execution.

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Ch3: Operating System Structure

  • 1. Silberschatz, Galvin and Gagne ©20023.1 Chapter 3: Operating-System Structures System Components Operating System Services System Calls System Programs System Structure Virtual Machines System Design and Implementation System Generation
  • 2. Silberschatz, Galvin and Gagne ©20023.2 Common System Components Process Management Main Memory Management File Management I/O System Management Secondary Management Networking Protection System Command-Interpreter System
  • 3. Silberschatz, Galvin and Gagne ©20023.3 Process Management A process is a program in execution. A process needs certain resources, including CPU time, memory, files, and I/O devices, to accomplish its task. The operating system is responsible for the following activities in connection with process management. Process creation and deletion. process suspension and resumption. Provision of mechanisms for: process synchronization process communication
  • 4. Silberschatz, Galvin and Gagne ©20023.4 Main-Memory Management Memory is a large array of words or bytes, each with its own address. It is a repository of quickly accessible data shared by the CPU and I/O devices. Main memory is a volatile storage device. It loses its contents in the case of system failure. The operating system is responsible for the following activities in connections with memory management: Keep track of which parts of memory are currently being used and by whom. Decide which processes to load when memory space becomes available. Allocate and deallocate memory space as needed.
  • 5. Silberschatz, Galvin and Gagne ©20023.5 File Management A file is a collection of related information defined by its creator. Commonly, files represent programs (both source and object forms) and data. The operating system is responsible for the following activities in connections with file management: File creation and deletion. Directory creation and deletion. Support of primitives for manipulating files and directories. Mapping files onto secondary storage. File backup on stable (nonvolatile) storage media.
  • 6. Silberschatz, Galvin and Gagne ©20023.6 I/O System Management The I/O system consists of: A buffer-caching system A general device-driver interface Drivers for specific hardware devices
  • 7. Silberschatz, Galvin and Gagne ©20023.7 Secondary-Storage Management Since main memory (primary storage) is volatile and too small to accommodate all data and programs permanently, the computer system must provide secondary storage to back up main memory. Most modern computer systems use disks as the principle on-line storage medium, for both programs and data. The operating system is responsible for the following activities in connection with disk management: Free space management Storage allocation Disk scheduling
  • 8. Silberschatz, Galvin and Gagne ©20023.8 Networking (Distributed Systems) A distributed system is a collection processors that do not share memory or a clock. Each processor has its own local memory. The processors in the system are connected through a communication network. Communication takes place using a protocol. A distributed system provides user access to various system resources. Access to a shared resource allows: Computation speed-up Increased data availability Enhanced reliability
  • 9. Silberschatz, Galvin and Gagne ©20023.9 Protection System Protection refers to a mechanism for controlling access by programs, processes, or users to both system and user resources. The protection mechanism must: distinguish between authorized and unauthorized usage. specify the controls to be imposed. provide a means of enforcement.
  • 10. Silberschatz, Galvin and Gagne ©20023.10 Command-Interpreter System Many commands are given to the operating system by control statements which deal with: process creation and management I/O handling secondary-storage management main-memory management file-system access protection networking
  • 11. Silberschatz, Galvin and Gagne ©20023.11 Command-Interpreter System (Cont.) The program that reads and interprets control statements is called variously: command-line interpreter shell (in UNIX) Its function is to get and execute the next command statement.
  • 12. Silberschatz, Galvin and Gagne ©20023.12 Operating System Services Program execution – system capability to load a program into memory and to run it. I/O operations – since user programs cannot execute I/O operations directly, the operating system must provide some means to perform I/O. File-system manipulation – program capability to read, write, create, and delete files. Communications – exchange of information between processes executing either on the same computer or on different systems tied together by a network. Implemented via shared memory or message passing. Error detection – ensure correct computing by detecting errors in the CPU and memory hardware, in I/O devices, or in user programs.
  • 13. Silberschatz, Galvin and Gagne ©20023.13 Additional Operating System Functions Additional functions exist not for helping the user, but rather for ensuring efficient system operations. • Resource allocation – allocating resources to multiple users or multiple jobs running at the same time. • Accounting – keep track of and record which users use how much and what kinds of computer resources for account billing or for accumulating usage statistics. • Protection – ensuring that all access to system resources is controlled.
  • 14. Silberschatz, Galvin and Gagne ©20023.14 System Calls System calls provide the interface between a running program and the operating system. Generally available as assembly-language instructions. Languages defined to replace assembly language for systems programming allow system calls to be made directly (e.g., C, C++) Three general methods are used to pass parameters between a running program and the operating system. Pass parameters in registers. Store the parameters in a table in memory, and the table address is passed as a parameter in a register. Push (store) the parameters onto the stack by the program, and pop off the stack by operating system.
  • 15. Silberschatz, Galvin and Gagne ©20023.15 Passing of Parameters As A Table
  • 16. Silberschatz, Galvin and Gagne ©20023.16 Types of System Calls Process control File management Device management Information maintenance Communications
  • 17. Silberschatz, Galvin and Gagne ©20023.17 MS-DOS Execution At System Start-up Running a Program
  • 18. Silberschatz, Galvin and Gagne ©20023.18 UNIX Running Multiple Programs
  • 19. Silberschatz, Galvin and Gagne ©20023.19 Communication Models Msg Passing Shared Memory Communication may take place using either message passing or shared memory.
  • 20. Silberschatz, Galvin and Gagne ©20023.20 System Programs System programs provide a convenient environment for program development and execution. The can be divided into: 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.
  • 21. Silberschatz, Galvin and Gagne ©20023.21 MS-DOS System Structure MS-DOS – written to provide the most functionality in the least space not divided into modules Although MS-DOS has some structure, its interfaces and levels of functionality are not well separated
  • 22. Silberschatz, Galvin and Gagne ©20023.22 MS-DOS Layer Structure
  • 23. Silberschatz, Galvin and Gagne ©20023.23 UNIX System Structure UNIX – limited by hardware functionality, the original UNIX operating system had limited structuring. The UNIX OS consists of two separable parts. Systems programs The kernel Consists of everything below the system-call interface and above the physical hardware Provides the file system, CPU scheduling, memory management, and other operating-system functions; a large number of functions for one level.
  • 24. Silberschatz, Galvin and Gagne ©20023.24 UNIX System Structure
  • 25. Silberschatz, Galvin and Gagne ©20023.25 Layered Approach The operating system is divided into a number of layers (levels), each built on top of lower layers. The bottom layer (layer 0), is the hardware; the highest (layer N) is the user interface. With modularity, layers are selected such that each uses functions (operations) and services of only lower-level layers.
  • 26. Silberschatz, Galvin and Gagne ©20023.26 An Operating System Layer
  • 27. Silberschatz, Galvin and Gagne ©20023.27 OS/2 Layer Structure
  • 28. Silberschatz, Galvin and Gagne ©20023.28 Microkernel System Structure Moves as much from the kernel into “user” space. Communication takes place between user modules using message passing. 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
  • 29. Silberschatz, Galvin and Gagne ©20023.29 Windows NT Client-Server Structure
  • 30. Silberschatz, Galvin and Gagne ©20023.30 Virtual Machines A virtual machine takes the layered approach to its logical conclusion. It treats hardware and the operating system kernel as though they were all hardware. A virtual machine provides an interface identical to the underlying bare hardware. The operating system creates the illusion of multiple processes, each executing on its own processor with its own (virtual) memory.
  • 31. Silberschatz, Galvin and Gagne ©20023.31 Virtual Machines (Cont.) The resources of the physical computer are shared to create the virtual machines. CPU scheduling can create the appearance that users have their own processor. Spooling and a file system can provide virtual card readers and virtual line printers. A normal user time-sharing terminal serves as the virtual machine operator’s console.
  • 32. Silberschatz, Galvin and Gagne ©20023.32 System Models Non-virtual Machine Virtual Machine
  • 33. Silberschatz, Galvin and Gagne ©20023.33 Advantages/Disadvantages of Virtual Machine The virtual-machine concept provides complete protection of system resources since each virtual machine is isolated from all other virtual machines. This isolation, however, permits no direct sharing of resources. A virtual-machine system is a perfect vehicle for operating-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 implement due to the effort required to provide an exact duplicate to the underlying machine.
  • 34. Silberschatz, Galvin and Gagne ©20023.34 Java Virtual Machine Compiled Java programs are platform-neutral bytecodes executed by a Java Virtual Machine (JVM). JVM consists of - class loader - class verifier - runtime interpreter Just-In-Time (JIT) compilers increase performance
  • 35. Silberschatz, Galvin and Gagne ©20023.35 Java Virtual Machine
  • 36. Silberschatz, Galvin and Gagne ©20023.36 System Design Goals User goals – operating system should be convenient to use, easy to learn, reliable, safe, and fast. System goals – operating system should be easy to design, implement, and maintain, as well as flexible, reliable, error-free, and efficient.
  • 37. Silberschatz, Galvin and Gagne ©20023.37 Mechanisms and Policies 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 policy decisions are to be changed later.
  • 38. Silberschatz, Galvin and Gagne ©20023.38 System Implementation Traditionally written in assembly language, operating systems can now be written in higher-level languages. Code written in a high-level language: can be written faster. is more compact. is easier to understand and debug. An operating system is far easier to port (move to some other hardware) if it is written in a high-level language.
  • 39. Silberschatz, Galvin and Gagne ©20023.39 System Generation (SYSGEN) Operating systems are designed to run on any of a class of machines; the system must be configured for each specific computer site. SYSGEN program obtains information concerning the specific configuration of the hardware system. Booting – starting a computer by loading the kernel. Bootstrap program – code stored in ROM that is able to locate the kernel, load it into memory, and start its execution.