Learn Reusable Resource definition in operating system with explanation to study “What is Reusable Resource”. Study reusable resource explanation with operating system terms to review operating system course for online degree programs.
Reusable Resource Definition
A resource that can be safely used by only one process at a time and is not depleted by that use.
Operating Systems by William Stallings
Reusable Resource Explanation
A reusable resource is a resource that is not rendered useless by being used. For instance, a magnetic disk such as hard drive or solid state drive is a reusable resource as it is not wasted if you use it once.
Dec 05, 2020 The operating system acts as the manager of these resources and allocates them to specific programs and users as necessary for their tasks. Therefore we can say an operating system is a resource allocator. This is the main features of an operating system. When a number of computers connected through a network more than one computers trying for. . Operating Limitations – Based on current operating conditions, such as, coolers out of service, etc. 4.1.3 Rating Methodology. Normal ratings are established based on design, test or actual operation; manufacturer nameplate and capability curves. There are no ratings above normal ratings. Serially reusable execution memory Download PDF Info Publication number US5987580A. US5987580A US08/835,160 US83516097A US5987580A US 5987580 A US5987580 A US. Resource is not directly under the control of the operating system, by the use of the primitive P and V operations introduced by Dijkstra 1. The facilities for queueing requests from separate tasks for a serially reusable resource provided in OS/360 by the ENQ and DEQ macros 2 are examples of.
Serially Reusable Resources In Operating System Diagram
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Serially Reusable Resources In Operating System
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Chapter 1: Introduction
Chapter 1: Introduction ■ What Operating Systems Do ■ ComputerSystem Organization ■ ComputerSystem Architecture ■ OperatingSystem Structure ■ OperatingSystem Operations ■ Process Management ■ Memory Management ■ Storage Management ■ Protection and Security ■ Distributed Systems ■ SpecialPurpose Systems ■ Computing Environments
Operating System Concepts – 7th Edition, Jan 12, 2005
1.2
Silberschatz, Galvin and Gagne ©2005
Objectives ■ To provide a grand tour of the major operating systems
components
■ To provide coverage of basic computer system organization
Operating System Concepts – 7th Edition, Jan 12, 2005
1.3
Silberschatz, Galvin and Gagne ©2005
What is an Operating System? ■ A program that acts as an intermediary between a user of a
computer and the computer hardware.
■ Operating system goals: ●
●
Execute user programs and make solving user problems easier. Make the computer system convenient to use.
■ Use the computer hardware in an efficient manner.
Operating System Concepts – 7th Edition, Jan 12, 2005
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Computer System Structure ■ Computer system can be divided into four components ●
Hardware – provides basic computing resources
●
Operating system
●
Controls and coordinates use of hardware among various applications and users
Application programs – define the ways in which the system resources are used to solve the computing problems of the users
●
CPU, memory, I/O devices
Word processors, compilers, web browsers, database systems, video games
Users
People, machines, other computers
Operating System Concepts – 7th Edition, Jan 12, 2005
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Four Components of a Computer System
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Operating System Definition ■ OS is a resource allocator ● ●
Manages all resources Decides between conflicting requests for efficient and fair resource use
■ OS is a control program ●
Controls execution of programs to prevent errors and improper use of the computer
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Operating System Definition (Cont.) ■ No universally accepted definition ■ “Everything a vendor ships when you order an operating system”
is good approximation ●
But varies wildly
■ “The one program running at all times on the computer” is the
kernel. Everything else is either a system program (ships with the operating system) or an application program
Operating System Concepts – 7th Edition, Jan 12, 2005
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Computer Startup ■ bootstrap program is loaded at powerup or reboot ●
Typically stored in ROM or EPROM, generally known as firmware
●
Initializates all aspects of system
●
Loads operating system kernel and starts execution
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Computer System Organization ■ Computersystem operation ●
●
One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles
Operating System Concepts – 7th Edition, Jan 12, 2005
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ComputerSystem Operation ■ I/O devices and the CPU can execute concurrently. ■ Each device controller is in charge of a particular device type. ■ Each device controller has a local buffer. ■ CPU moves data from/to main memory to/from local buffers ■ I/O is from the device to local buffer of controller. ■ Device controller informs CPU that it has finished its operation by
causing an interrupt.
Operating System Concepts – 7th Edition, Jan 12, 2005
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Silberschatz, Galvin and Gagne ©2005
Common Functions of Interrupts ■ Interrupt transfers control to the interrupt service routine generally,
through the interrupt vector, which contains the addresses of all the service routines.
■ Interrupt architecture must save the address of the interrupted
instruction.
■ Incoming interrupts are disabled while another interrupt is being
processed to prevent a lost interrupt.
■ A trap is a softwaregenerated interrupt caused either by an error or
a user request.
■ An operating system is interrupt driven.
Operating System Concepts – 7th Edition, Jan 12, 2005
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Silberschatz, Galvin and Gagne ©2005
Interrupt Handling ■ The operating system preserves the state of the CPU by storing
registers and the program counter.
■ Determines which type of interrupt has occurred: ●
polling
●
vectored interrupt system
■ Separate segments of code determine what action should be taken
for each type of interrupt
Operating System Concepts – 7th Edition, Jan 12, 2005
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Silberschatz, Galvin and Gagne ©2005
Interrupt Timeline
Operating System Concepts – 7th Edition, Jan 12, 2005
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I/O Structure ■ After I/O starts, control returns to user program only upon I/O
completion. ●
Wait instruction idles the CPU until the next interrupt
●
Wait loop (contention for memory access).
●
At most one I/O request is outstanding at a time, no simultaneous I/O processing.
■ After I/O starts, control returns to user program without waiting
for I/O completion. ● ● ●
System call – request to the operating system to allow user to wait for I/O completion. Devicestatus table contains entry for each I/O device indicating its type, address, and state. Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.
Operating System Concepts – 7th Edition, Jan 12, 2005
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Two I/O Methods Synchronous
Operating System Concepts – 7th Edition, Jan 12, 2005
Asynchronous
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DeviceStatus Table
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Direct Memory Access Structure ■ Used for highspeed I/O devices able to transmit information at
close to memory speeds.
■ Device controller transfers blocks of data from buffer storage
directly to main memory without CPU intervention.
■ Only one interrupt is generated per block, rather than the one
interrupt per byte.
Operating System Concepts – 7th Edition, Jan 12, 2005
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Storage Structure ■ Main memory – only large storage media that the CPU can access
directly.
■ Secondary storage – extension of main memory that provides large
nonvolatile storage capacity.
■ Magnetic disks – rigid metal or glass platters covered with magnetic
recording material ●
●
Disk surface is logically divided into tracks, which are subdivided into sectors. The disk controller determines the logical interaction between the device and the computer.
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Storage Hierarchy ■ Storage systems organized in hierarchy. ●
Speed
●
Cost
●
Volatility
■ Caching – copying information into faster storage system; main
memory can be viewed as a last cache for secondary storage.
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StorageDevice Hierarchy
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Caching ■ Important principle, performed at many levels in a computer (in
hardware, operating system, software)
■ Information in use copied from slower to faster storage temporarily ■ Faster storage (cache) checked first to determine if information is
there ●
If it is, information used directly from the cache (fast)
●
If not, data copied to cache and used there
■ Cache smaller than storage being cached ●
Cache management important design problem
●
Cache size and replacement policy
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Performance of Various Levels of Storage ■ Movement between levels of storage hierarchy can be explicit or
implicit
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Migration of Integer A from Disk to Register ■ Multitasking environments must be careful to use most recent
value, no matter where it is stored in the storage hierarchy
■ Multiprocessor environment must provide cache coherency in
hardware such that all CPUs have the most recent value in their cache
■ Distributed environment situation even more complex ●
Several copies of a datum can exist
●
Various solutions covered in Chapter 17
Operating System Concepts – 7th Edition, Jan 12, 2005
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Operating System Structure ■
Multiprogramming needed for efficiency ● ●
■
Single user cannot keep CPU and I/O devices busy at all times Multiprogramming organizes jobs (code and data) so CPU always has one to execute
●
A subset of total jobs in system is kept in memory
●
One job selected and run via job scheduling
●
When it has to wait (for I/O for example), OS switches to another job
Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing ●
Response time should be < 1 second
●
Each user has at least one program executing in memory process
●
If several jobs ready to run at the same time CPU scheduling
● ●
If processes don’t fit in memory, swapping moves them in and out to run Virtual memory allows execution of processes not completely in memory
Operating System Concepts – 7th Edition, Jan 12, 2005
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Silberschatz, Galvin and Gagne ©2005
Memory Layout for Multiprogrammed System
Operating System Concepts – 7th Edition, Jan 12, 2005
1.26
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OperatingSystem Operations ■ Interrupt driven by hardware ■ Software error or request creates exception or trap ●
Division by zero, request for operating system service
■ Other process problems include infinite loop, processes modifying
each other or the operating system
■ Dualmode operation allows OS to protect itself and other system
components ●
User mode and kernel mode
●
Mode bit provided by hardware
Provides ability to distinguish when system is running user code or kernel code Some instructions designated as privileged, only executable in kernel mode System call changes mode to kernel, return from call resets it to user
Operating System Concepts – 7th Edition, Jan 12, 2005
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Silberschatz, Galvin and Gagne ©2005
Transition from User to Kernel Mode ■ Timer to prevent infinite loop / process hogging resources ●
Set interrupt after specific period
●
Operating system decrements counter
●
When counter zero generate an interrupt
●
Set up before scheduling process to regain control or terminate program that exceeds allotted time
Operating System Concepts – 7th Edition, Jan 12, 2005
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Process Management ■
A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity.
■
Process needs resources to accomplish its task ●
CPU, memory, I/O, files
●
Initialization data
■
Process termination requires reclaim of any reusable resources
■
Singlethreaded process has one program counter specifying location of next instruction to execute ●
Process executes instructions sequentially, one at a time, until completion
■
Multithreaded process has one program counter per thread
■
Typically system has many processes, some user, some operating system running concurrently on one or more CPUs ●
Concurrency by multiplexing the CPUs among the processes / threads
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Process Management Activities The operating system is responsible for the following activities in connection with process management: ■ Creating and deleting both user and system processes ■ Suspending and resuming processes ■ Providing mechanisms for process synchronization ■ Providing mechanisms for process communication ■ Providing mechanisms for deadlock handling
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Memory Management ■ All data in memory before and after processing ■ All instructions in memory in order to execute ■ Memory management determines what is in memory when ●
Optimizing CPU utilization and computer response to users
■ Memory management activities ●
●
●
Keeping track of which parts of memory are currently being used and by whom Deciding which processes (or parts thereof) and data to move into and out of memory Allocating and deallocating memory space as needed
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Storage Management ■ OS provides uniform, logical view of information storage ●
Abstracts physical properties to logical storage unit file
●
Each medium is controlled by device (i.e., disk drive, tape drive)
Varying properties include access speed, capacity, data transfer rate, access method (sequential or random)
■ FileSystem management ● ● ●
Files usually organized into directories Access control on most systems to determine who can access what OS activities include
Creating and deleting files and directories
Primitives to manipulate files and dirs
Mapping files onto secondary storage
Backup files onto stable (nonvolatile) storage media
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MassStorage Management ■
Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time.
■
Proper management is of central importance
■
Entire speed of computer operation hinges on disk subsystem and its algorithms
■
OS activities
■
●
Freespace management
●
Storage allocation
●
Disk scheduling
Some storage need not be fast ●
Tertiary storage includes optical storage, magnetic tape
●
Still must be managed
●
Varies between WORM (writeonce, readmanytimes) and RW (read write)
Operating System Concepts – 7th Edition, Jan 12, 2005
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I/O Subsystem ■ One purpose of OS is to hide peculiarities of hardware devices
from the user
■ I/O subsystem responsible for ●
Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs)
●
General devicedriver interface
●
Drivers for specific hardware devices
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Protection and Security ■ Protection – any mechanism for controlling access of processes or
users to resources defined by the OS
■ Security – defense of the system against internal and external
attacks ●
Huge range, including denialofservice, worms, viruses, identity theft, theft of service
■ Systems generally first distinguish among users, to determine who
can do what ● ● ●
●
User identities (user IDs, security IDs) include name and associated number, one per user User ID then associated with all files, processes of that user to determine access control Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file Privilege escalation allows user to change to effective ID with more rights
Operating System Concepts – 7th Edition, Jan 12, 2005
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Computing Environments ■ Traditional computer ●
Blurring over time
●
Office environment PCs connected to a network, terminals attached to
mainframe or minicomputers providing batch and timesharing
Now portals allowing networked and remote systems
access to same resources
●
Home networks Used to be single system, then modems Now firewalled, networked
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Computing Environments (Cont.) ■
ClientServer Computing ● ●
Dumb terminals supplanted by smart PCs Many systems now servers, responding to requests generated by clients
Computeserver provides an interface to client to request services (i.e. database) Fileserver provides interface for clients to store and retrieve files
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PeertoPeer Computing ■ Another model of distributed system ■ P2P does not distinguish clients and servers ●
Instead all nodes are considered peers
●
May each act as client, server or both
●
Node must join P2P network
●
Registers its service with central lookup service on network, or Broadcast request for service and respond to requests for service via discovery protocol
Examples include Napster and Gnutella
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WebBased Computing ■ Web has become ubiquitous ■ PCs most prevalent devices ■ More devices becoming networked to allow web access ■ New category of devices to manage web traffic among similar
servers: load balancers
■ Use of operating systems like Windows 95, clientside, have
evolved into Linux and Windows XP, which can be clients and servers
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End of Chapter 1
Chapter 1: Introduction ■ What Operating Systems Do ■ ComputerSystem Organization ■ ComputerSystem Architecture ■ OperatingSystem Structure ■ OperatingSystem Operations ■ Process Management ■ Memory Management ■ Storage Management ■ Protection and Security ■ Distributed Systems ■ SpecialPurpose Systems ■ Computing Environments
Operating System Concepts – 7th Edition, Jan 12, 2005
1.2
Silberschatz, Galvin and Gagne ©2005
Objectives ■ To provide a grand tour of the major operating systems
components
■ To provide coverage of basic computer system organization
Operating System Concepts – 7th Edition, Jan 12, 2005
1.3
Silberschatz, Galvin and Gagne ©2005
What is an Operating System? ■ A program that acts as an intermediary between a user of a
computer and the computer hardware.
■ Operating system goals: ●
●
Execute user programs and make solving user problems easier. Make the computer system convenient to use.
■ Use the computer hardware in an efficient manner.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.4
Silberschatz, Galvin and Gagne ©2005
Computer System Structure ■ Computer system can be divided into four components ●
Hardware – provides basic computing resources
●
Operating system
●
Controls and coordinates use of hardware among various applications and users
Application programs – define the ways in which the system resources are used to solve the computing problems of the users
●
CPU, memory, I/O devices
Word processors, compilers, web browsers, database systems, video games
Users
People, machines, other computers
Operating System Concepts – 7th Edition, Jan 12, 2005
1.5
Silberschatz, Galvin and Gagne ©2005
Four Components of a Computer System
Operating System Concepts – 7th Edition, Jan 12, 2005
1.6
Silberschatz, Galvin and Gagne ©2005
Operating System Definition ■ OS is a resource allocator ● ●
Manages all resources Decides between conflicting requests for efficient and fair resource use
■ OS is a control program ●
Controls execution of programs to prevent errors and improper use of the computer
Operating System Concepts – 7th Edition, Jan 12, 2005
1.7
Silberschatz, Galvin and Gagne ©2005
Operating System Definition (Cont.) ■ No universally accepted definition ■ “Everything a vendor ships when you order an operating system”
is good approximation ●
But varies wildly
■ “The one program running at all times on the computer” is the
kernel. Everything else is either a system program (ships with the operating system) or an application program
Operating System Concepts – 7th Edition, Jan 12, 2005
1.8
Silberschatz, Galvin and Gagne ©2005
Computer Startup ■ bootstrap program is loaded at powerup or reboot ●
Typically stored in ROM or EPROM, generally known as firmware
●
Initializates all aspects of system
●
Loads operating system kernel and starts execution
Operating System Concepts – 7th Edition, Jan 12, 2005
1.9
Silberschatz, Galvin and Gagne ©2005
Computer System Organization ■ Computersystem operation ●
●
One or more CPUs, device controllers connect through common bus providing access to shared memory Concurrent execution of CPUs and devices competing for memory cycles
Operating System Concepts – 7th Edition, Jan 12, 2005
1.10
Silberschatz, Galvin and Gagne ©2005
ComputerSystem Operation ■ I/O devices and the CPU can execute concurrently. ■ Each device controller is in charge of a particular device type. ■ Each device controller has a local buffer. ■ CPU moves data from/to main memory to/from local buffers ■ I/O is from the device to local buffer of controller. ■ Device controller informs CPU that it has finished its operation by
causing an interrupt.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.11
Silberschatz, Galvin and Gagne ©2005
Common Functions of Interrupts ■ Interrupt transfers control to the interrupt service routine generally,
through the interrupt vector, which contains the addresses of all the service routines.
■ Interrupt architecture must save the address of the interrupted
instruction.
■ Incoming interrupts are disabled while another interrupt is being
processed to prevent a lost interrupt.
■ A trap is a softwaregenerated interrupt caused either by an error or
a user request.
■ An operating system is interrupt driven.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.12
Silberschatz, Galvin and Gagne ©2005
Interrupt Handling ■ The operating system preserves the state of the CPU by storing
registers and the program counter.
■ Determines which type of interrupt has occurred: ●
polling
●
vectored interrupt system
■ Separate segments of code determine what action should be taken
for each type of interrupt
Operating System Concepts – 7th Edition, Jan 12, 2005
1.13
Silberschatz, Galvin and Gagne ©2005
Interrupt Timeline
Operating System Concepts – 7th Edition, Jan 12, 2005
1.14
Silberschatz, Galvin and Gagne ©2005
I/O Structure ■ After I/O starts, control returns to user program only upon I/O
completion. ●
Wait instruction idles the CPU until the next interrupt
●
Wait loop (contention for memory access).
●
At most one I/O request is outstanding at a time, no simultaneous I/O processing.
■ After I/O starts, control returns to user program without waiting
for I/O completion. ● ● ●
System call – request to the operating system to allow user to wait for I/O completion. Devicestatus table contains entry for each I/O device indicating its type, address, and state. Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.15
Silberschatz, Galvin and Gagne ©2005
Two I/O Methods Synchronous
Operating System Concepts – 7th Edition, Jan 12, 2005
Asynchronous
1.16
Silberschatz, Galvin and Gagne ©2005
DeviceStatus Table
Operating System Concepts – 7th Edition, Jan 12, 2005
1.17
Silberschatz, Galvin and Gagne ©2005
Direct Memory Access Structure ■ Used for highspeed I/O devices able to transmit information at
close to memory speeds.
■ Device controller transfers blocks of data from buffer storage
directly to main memory without CPU intervention.
■ Only one interrupt is generated per block, rather than the one
interrupt per byte.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.18
Silberschatz, Galvin and Gagne ©2005
Storage Structure ■ Main memory – only large storage media that the CPU can access
directly.
■ Secondary storage – extension of main memory that provides large
nonvolatile storage capacity.
■ Magnetic disks – rigid metal or glass platters covered with magnetic
recording material ●
●
Disk surface is logically divided into tracks, which are subdivided into sectors. The disk controller determines the logical interaction between the device and the computer.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.19
Silberschatz, Galvin and Gagne ©2005
Storage Hierarchy ■ Storage systems organized in hierarchy. ●
Speed
●
Cost
●
Volatility
■ Caching – copying information into faster storage system; main
memory can be viewed as a last cache for secondary storage.
Operating System Concepts – 7th Edition, Jan 12, 2005
1.20
Silberschatz, Galvin and Gagne ©2005
StorageDevice Hierarchy
Operating System Concepts – 7th Edition, Jan 12, 2005
1.21
Silberschatz, Galvin and Gagne ©2005
Caching ■ Important principle, performed at many levels in a computer (in
hardware, operating system, software)
■ Information in use copied from slower to faster storage temporarily ■ Faster storage (cache) checked first to determine if information is
there ●
If it is, information used directly from the cache (fast)
●
If not, data copied to cache and used there
■ Cache smaller than storage being cached ●
Cache management important design problem
●
Cache size and replacement policy
Operating System Concepts – 7th Edition, Jan 12, 2005
1.22
Silberschatz, Galvin and Gagne ©2005
Performance of Various Levels of Storage ■ Movement between levels of storage hierarchy can be explicit or
implicit
Operating System Concepts – 7th Edition, Jan 12, 2005
1.23
Silberschatz, Galvin and Gagne ©2005
Migration of Integer A from Disk to Register ■ Multitasking environments must be careful to use most recent
value, no matter where it is stored in the storage hierarchy
■ Multiprocessor environment must provide cache coherency in
hardware such that all CPUs have the most recent value in their cache
■ Distributed environment situation even more complex ●
Several copies of a datum can exist
●
Various solutions covered in Chapter 17
Operating System Concepts – 7th Edition, Jan 12, 2005
1.24
Silberschatz, Galvin and Gagne ©2005
Operating System Structure ■
Multiprogramming needed for efficiency ● ●
■
Single user cannot keep CPU and I/O devices busy at all times Multiprogramming organizes jobs (code and data) so CPU always has one to execute
●
A subset of total jobs in system is kept in memory
●
One job selected and run via job scheduling
●
When it has to wait (for I/O for example), OS switches to another job
Timesharing (multitasking) is logical extension in which CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing ●
Response time should be < 1 second
●
Each user has at least one program executing in memory process
●
If several jobs ready to run at the same time CPU scheduling
● ●
If processes don’t fit in memory, swapping moves them in and out to run Virtual memory allows execution of processes not completely in memory
Operating System Concepts – 7th Edition, Jan 12, 2005
1.25
Silberschatz, Galvin and Gagne ©2005
Memory Layout for Multiprogrammed System
Operating System Concepts – 7th Edition, Jan 12, 2005
1.26
Silberschatz, Galvin and Gagne ©2005
OperatingSystem Operations ■ Interrupt driven by hardware ■ Software error or request creates exception or trap ●
Division by zero, request for operating system service
■ Other process problems include infinite loop, processes modifying
each other or the operating system
■ Dualmode operation allows OS to protect itself and other system
components ●
User mode and kernel mode
●
Mode bit provided by hardware
Provides ability to distinguish when system is running user code or kernel code Some instructions designated as privileged, only executable in kernel mode System call changes mode to kernel, return from call resets it to user
Operating System Concepts – 7th Edition, Jan 12, 2005
1.27
Silberschatz, Galvin and Gagne ©2005
Transition from User to Kernel Mode ■ Timer to prevent infinite loop / process hogging resources ●
Set interrupt after specific period
●
Operating system decrements counter
●
When counter zero generate an interrupt
●
Set up before scheduling process to regain control or terminate program that exceeds allotted time
Operating System Concepts – 7th Edition, Jan 12, 2005
1.28
Silberschatz, Galvin and Gagne ©2005
Process Management ■
A process is a program in execution. It is a unit of work within the system. Program is a passive entity, process is an active entity.
■
Process needs resources to accomplish its task ●
CPU, memory, I/O, files
●
Initialization data
■
Process termination requires reclaim of any reusable resources
■
Singlethreaded process has one program counter specifying location of next instruction to execute ●
Process executes instructions sequentially, one at a time, until completion
■
Multithreaded process has one program counter per thread
■
Typically system has many processes, some user, some operating system running concurrently on one or more CPUs ●
Concurrency by multiplexing the CPUs among the processes / threads
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Process Management Activities The operating system is responsible for the following activities in connection with process management: ■ Creating and deleting both user and system processes ■ Suspending and resuming processes ■ Providing mechanisms for process synchronization ■ Providing mechanisms for process communication ■ Providing mechanisms for deadlock handling
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Memory Management ■ All data in memory before and after processing ■ All instructions in memory in order to execute ■ Memory management determines what is in memory when ●
Optimizing CPU utilization and computer response to users
■ Memory management activities ●
●
●
Keeping track of which parts of memory are currently being used and by whom Deciding which processes (or parts thereof) and data to move into and out of memory Allocating and deallocating memory space as needed
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Storage Management ■ OS provides uniform, logical view of information storage ●
Abstracts physical properties to logical storage unit file
●
Each medium is controlled by device (i.e., disk drive, tape drive)
Varying properties include access speed, capacity, data transfer rate, access method (sequential or random)
■ FileSystem management ● ● ●
Files usually organized into directories Access control on most systems to determine who can access what OS activities include
Creating and deleting files and directories
Primitives to manipulate files and dirs
Mapping files onto secondary storage
Backup files onto stable (nonvolatile) storage media
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MassStorage Management ■
Usually disks used to store data that does not fit in main memory or data that must be kept for a “long” period of time.
■
Proper management is of central importance
■
Entire speed of computer operation hinges on disk subsystem and its algorithms
■
OS activities
■
●
Freespace management
●
Storage allocation
●
Disk scheduling
Some storage need not be fast ●
Tertiary storage includes optical storage, magnetic tape
●
Still must be managed
●
Varies between WORM (writeonce, readmanytimes) and RW (read write)
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I/O Subsystem ■ One purpose of OS is to hide peculiarities of hardware devices
from the user
■ I/O subsystem responsible for ●
Memory management of I/O including buffering (storing data temporarily while it is being transferred), caching (storing parts of data in faster storage for performance), spooling (the overlapping of output of one job with input of other jobs)
●
General devicedriver interface
●
Drivers for specific hardware devices
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Protection and Security ■ Protection – any mechanism for controlling access of processes or
users to resources defined by the OS
■ Security – defense of the system against internal and external
attacks ●
Huge range, including denialofservice, worms, viruses, identity theft, theft of service
■ Systems generally first distinguish among users, to determine who
can do what ● ● ●
●
User identities (user IDs, security IDs) include name and associated number, one per user User ID then associated with all files, processes of that user to determine access control Group identifier (group ID) allows set of users to be defined and controls managed, then also associated with each process, file Privilege escalation allows user to change to effective ID with more rights
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Computing Environments ■ Traditional computer ●
Blurring over time
●
Office environment PCs connected to a network, terminals attached to
mainframe or minicomputers providing batch and timesharing
Now portals allowing networked and remote systems
access to same resources
●
Home networks Used to be single system, then modems Now firewalled, networked
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Computing Environments (Cont.) ■
ClientServer Computing ● ●
Dumb terminals supplanted by smart PCs Many systems now servers, responding to requests generated by clients
Computeserver provides an interface to client to request services (i.e. database) Fileserver provides interface for clients to store and retrieve files
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PeertoPeer Computing ■ Another model of distributed system ■ P2P does not distinguish clients and servers ●
Instead all nodes are considered peers
●
May each act as client, server or both
●
Node must join P2P network
●
Registers its service with central lookup service on network, or Broadcast request for service and respond to requests for service via discovery protocol
Examples include Napster and Gnutella
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WebBased Computing ■ Web has become ubiquitous ■ PCs most prevalent devices ■ More devices becoming networked to allow web access ■ New category of devices to manage web traffic among similar
servers: load balancers
■ Use of operating systems like Windows 95, clientside, have
evolved into Linux and Windows XP, which can be clients and servers
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End of Chapter 1