Ch03 Operating-System Structures 2
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Transcript of Ch03 Operating-System Structures 2
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Silberschatz, Galvin and Gagne 20021 / 42Operating System Concepts
Chapter 3: Operating-System Structures
3.1 System Components
3.2 Operating System Services
3.3 System Calls
3.4 System Programs
3.5 System Structure
3.6 Virtual Machines
3.7 System Design and Implementation 3.8 System Generation
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3.1 System Components
3.1.1 Process Management
3.1.2 Main Memory Management
3.1.3 File Management
3.1.4 I/O System Management
3.1.5 Secondary Management 3.1.6 Networking
3.1.7 Protection System
3.1.8 Command-Interpreter System
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3.1.1 Process Management
Aprocess is a program in execution. A processneeds certain resources, including CPU time,memory, files, and I/O devices, to accomplish
its task.
The operating system is responsible for thefollowing activities in connection with process
management. Process creation and deletion.
process suspension and resumption.
Provision of mechanisms for:
process synchronization process communication
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3.1.2 Main-Memory Management
Memory is a large array of words or bytes, eachwith its own address. It is a repository ofquickly 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 thefollowing activities in connections with memorymanagement: 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.
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3.1.3 File Management
A file is a collection of related information
defined by its creator. Commonly, filesrepresent programs (both source and objectforms) and data.
The operating system is responsible for the
following activities in connections with filemanagement: 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.
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3.1.4 I/O System Management
The I/O system consists of:
A buffer-caching systemA general device-driver interface
Drivers for specific hardware devices
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3.1.5 Secondary-Storage Management
Since main memory (primary storage) is volatileand too small to accommodate all data andprograms permanently, the computer system
must provide secondary storage to back upmain memory.
Most modern computer systems use disks asthe principle on-line storage medium, for bothprograms and data.
The operating system is responsible for thefollowing activities in connection with disk
management: Free space management
Storage allocation
Disk scheduling
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3.1.6 Networking (Distributed Systems)
A distributedsystem is a collection processors
that do not share memory or a clock. Eachprocessor has its own local memory.
The processors in the system are connectedthrough a communication network.
Communication takes place using aprotocol.
A distributed system provides user access tovarious system resources.
Access to a shared resource allows: Computation speed-up
Increased data availability
Enhanced reliability
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3.1.7 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.
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3.1.8 Command-Interpreter System
Many commands are given to the
operating system by control statementswhich deal with: process creation and management
I/O handling secondary-storage management
main-memory management
file-system access protection
networking
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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 thenext command statement.
3 2 O ti S t S i
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3.2 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 performI/O.
File-system manipulation program capabilityto read, write, create, and delete files.
Communications exchange of informationbetween processes executing either on thesame computer or on different systems tied
together by a network. Implemented via sharedmemoryor message passing.
Error detection ensure correct computing bydetecting errors in the CPU and memoryhardware, in I/O devices, or in user programs.
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Additional Operating System Functions
Additional functions exist not for helping
the user, but rather for ensuring efficient
system operations. Resource allocation allocating resources to multipleusers or multiple jobs running at the same time.
Accounting keep track of and record which usersuse how much and what kinds of computer resourcesfor account billing or for accumulating usage statistics.
Protection ensuring that all access to systemresources is controlled.
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3.3 System Calls
System calls provide the interface between arunning program and the operating system. Generally available as assembly-language instructions.
Languages defined to replace assembly language forsystems programming allow system calls to be made directly(e.g., C, C++)
Three general methods are used to passparameters between a running program andthe operating system. Pass parameters in registers.
Store the parameters in a table in memory, and the tableaddress is passed as a parameter in a register.
Push (store) the parameters onto the stackby the program,andpop off the stack by operating system.
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Fig 3.1 Passing of Parameters As A Table
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Types of System Calls
Process control
File management
Device management
Information maintenance Communications
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Fig 3.3 MS-DOS Execution
At System Start-up Running a Program
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Fig 3.4 UNIX Running Multiple Programs
Fi 3 5 C i ti M d l
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Fig 3.5 Communication Models
Communication may take place usingeither message passing or shared
memory.
Shared MemoryMsg Passing
3 4 S t P
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3.4 System Programs
System programs provide a convenientenvironment for program development andexecution. The programs 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 isdefined by system programs, not the actualsystem calls.
3 5 S t St t
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3.5 System Structure
3.5.1 Simple Structure
MS-DOS written to provide the mostfunctionality in the least space not divided into modules
Although MS-DOS has some structure, its interfacesand levels of functionality are not well separated
Fig 3 6 MS DOS La er Str ct re
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Fig 3.6 MS-DOS Layer Structure
UNIX System Structure
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UNIX System Structure
UNIX limited by hardware functionality,
the original UNIX operating system had
limited structuring. The UNIX OSconsists of two separable parts. Systems programs
The kernelConsists 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; alarge number of functions for one level.
Fig 3 7 UNIX System Structure
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Fig 3.7 UNIX System Structure
3 5 2 Layered Approach
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3.5.2 Layered Approach
The operating system is divided into a
number of layers (levels), each built ontop 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.
Fig 3 8 An Operating System Layer
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Fig 3.8 An Operating System Layer
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Layered Structure of the THE OS
A layered design was first used in THEoperating system. Its six layers are as
follows:
la ye r 5 : u se r p ro gra m s
la ye r 4 : b u ffe r in g fo r in p u t a n d o u t p u t
la ye r 3 : o p e ra to r -c o n s o le d e v ic e d rive r
la ye r 2 : m e m o ry m a na g em e nt
la ye r 1 : C P U s c h e d ulin g
la ye r 0 : h a rd w a re
Fig 3 9 OS/2 Layer Structure
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Fig 3.9 OS/2 Layer Structure
3 5 3 Microkernel System Structure
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3.5.3 Microkernel System Structure
Moves as much from the kernel into
Communication takes place between user
Benefits:- easier to extend a microkernel
- easier to port the operating system to
- more reliable (less code is running in
- more secure
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Fig 3.10 Windows NT Client-Server
Structure
3 6 Virtual Machines
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3.6 Virtual Machines
A virtual machine takes the layeredapproach to its logical conclusion. Ittreats hardware and the operating system
kernel as though they were all hardware.A virtual machine provides an interface
identicalto the underlying bare hardware.
The operating system creates the illusionof multiple processes, each executing onits own processor with its own (virtual)
memory.
Virtual Machines (Cont.)
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Virtual Machines (Cont.)
The resources of the physical computerare shared to create the virtual
machines.
CPU scheduling can create the appearancethat 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 operators console.
Fig 3.11 System Models
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Fig 3.11 System Models
Virtual MachineNon-virtual Machine
Advantages/Disadvantages of Virtual Machines
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g g
The virtual-machine concept provides completeprotection of system resources since each virtualmachine is isolated from all other virtual
machines. This isolation, however, permits nodirect sharing of resources.
A virtual-machine system is a perfect vehicle for
operating-systems research and development.System development is done on the virtualmachine, 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
exactduplicate to the underlying machine.
3.6.3 Java Virtual Machine
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Compiled Java programs are platform-
neutral bytecodes executed by a JavaVirtual Machine (JVM).
JVM consists of
- class loader- class verifier
- runtime interpreter
Just-In-Time (JIT) compilers increaseperformance
Fig 3.12 Java Virtual Machine
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g
3.7 System Design Goals
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3.7.1 Design GoalsUser 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.
3.7.2 Mechanisms and Policies
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Mechanisms determine how to do
something, policies decide what will bedone.
The separation of policy from
mechanism is a very important principle,it allows maximum flexibility if policy
decisions are to be changed later.
3.7.3 System Implementation
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y p
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 toport
(move to some other hardware) if it iswritten in a high-level language.
3.8 System Generation (SYSGEN)
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Operating systems are designed to run on any of aclass of machines; the system must be configured
for each specific computer site.
SYSGEN program obtains information concerningthe 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.
Exercises:
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3.6
3.7
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THE EN