os concepts an introduction
DESCRIPTION
operating systems. OS Concepts An Introduction. operating systems. At the end of this module, you should have a basic understanding of what an operating system is, what it does, and what the major components of an operating system are. operating systems. Why should I study - PowerPoint PPT PresentationTRANSCRIPT
OS ConceptsOS ConceptsAn IntroductionAn Introduction
OS ConceptsOS ConceptsAn IntroductionAn Introduction
operatingsystems
At the end of this module, you should have abasic understanding of what an operating system is, what it does, and what the major components of an operating system are.
operatingsystems
Why should I study operating systems?
operatingsystems
Based on a 2007 IT Salary Survey
Application Programmers System Programmers
Average SalaryAverage Salary $71,020$71,020 $79,300$79,300
Average BonusAverage Bonus $ 3,410$ 3,410 $ 3,940$ 3,940
Based on a 2007 IT Salary Survey
Application Programmers System Programmers
Average SalaryAverage Salary $71,020$71,020 $79,300$79,300
Average BonusAverage Bonus $ 3,410$ 3,410 $ 3,940$ 3,940
operatingsystems
Based on a 2007 IT Salary Survey
Application Programmers System Programmers
System Mainframe $74,100 $80,840 Unix/Linux $76,100 $84,100 Windows $71,000 $79,300
Based on a 2007 IT Salary Survey
Application Programmers System Programmers
System Mainframe $74,100 $80,840 Unix/Linux $76,100 $84,100 Windows $71,000 $79,300
operatingsystems
operatingsystems
Even as an application programmer, mostreal commercial applications will require that you
Understand OS design issues and tradeoffsPerformanceFunctionSpace
Be able to exploit OS capabilitiesMultiple ProcessesThreadsSynchronizationCommunication
What Is An Operating What Is An Operating SystemSystem
What Is An Operating What Is An Operating SystemSystem
CPU
Operating System Kernel
Language Libraries and System Calls API
System and Application Programs
User User Useroperatingsystems
personal computer mainframe system
cell phones
Music playersgame controllers
Hardware
Device Device Device
Operating System
ExecutingProgram
This program has no sense of sharing the system’s resources with other programs. It sees an Abstract Machine that has all of the resources that it needs.
The Abstract MachineThe Abstract MachineThe Abstract MachineThe Abstract MachineModern computing systems are multi-user, multi-programsystems. The fundamental task of an operating systemin this environment is to give each running program alogical, abstract machine that contains all of the resources that it needs to do its job.
Input/Output devicesMemoryCPUGeneral purpose registersStatus registersStack
ExecutionContext
Computer System Organization
system bus
cpu
diskcontroller
memory
devicecontroller
printer
devicecontroller
keyboard
. . .
app app app
Computer System Operation
system bus
cpu
diskcontroller
memory
devicecontroller
printer
devicecontroller
keyboard
. . .
cpu and deviceswork concurrently
Computer System Operation
system bus
cpu
diskcontroller
memory
devicecontroller
printer
devicecontroller
keyboard
. . .
each device controller is incharge of a particular devicetype
Computer System Operation
system bus
cpu
diskcontroller
memory
devicecontroller
printer
devicecontroller
keyboard
. . .Each device controllerhas a local buffer
Computer System Operation
system bus
cpu
diskcontroller
memory
devicecontroller
printer
devicecontroller
keyboard
. . .
device controllers send interrupts to the cpu to tell it that they have finished an operation the cpu told them to do
Interrupts
An interrupt causes control to branch to an interruptservice routine through an interrupt vector.
The address of the interrupted instruction is saved.
Incoming interrupts are disabled while an interruptis being processed.
A trap is a software generated interrupt.
An operating system is interrupt driven.
I/O Processing
Synchronous I/O
1. A process starts an I/O operation2. The requesting process waits until the I/O completes
requesting process
device driver
wait
interrupt handler
hardwaredata
I/O Processing
Asynchronous I/O
1. A process starts an I/O operation2. An acknowledgement is returned3. The process continues execution4. The device interrupts the process when the I/O is complete
requesting process
device driver
interrupt handler
hardwaredata
ProcessesProcessesProcessesProcesses
A process is defined as a program in execution.It includes * The program itself (program segment) * The program’s data (data segment, stack, heap) * Open files * The execution context
For efficiency, modern operating systems allowmany processes to be running concurrently.
When one process has to wait for something,typically for an I/O operation to complete, theoperating systems schedules another process to run.
Many programs can be in memory at the sametime. The operating system gives each processa slice of time in which to run.
ThreadsThreadsThreadsThreadsA thread, or thread of execution, is the set of instructionsbeing executed in a process.
In a single thread system each process has exactly one execution engine (the logical machine).
In a multi-thread environment, a process may have manyexecution engines, one for each thread. Thus, each thread has it’sown runtime stack, registers, and state information, but they all share the same address space in memory (program and data), and the same files.
In new multi-core machines, each logical engine may run on areal engine.
ResourcesResourcesResourcesResources
All of the components required for a program to do it’sjob are called resources.
* memory* cpu time* devices* files* network connection
When a process needs to use a resource, it must askthe operating system for the resource before using it.
Once a process asks for a resource, it suspends operationand waits until the resource is available.
Responsibilities of the Responsibilities of the OSOS
Responsibilities of the Responsibilities of the OSOS
1. Create an abstract machine environment for eachrunning process.
2. Manage the use of the physical components in the system, according to the policies of the system’s administrator or the system designer.
* Device management* Process and thread management* Memory Management* File Management
Device ManagementDevice ManagementDevice ManagementDevice Management
The OS manages the allocation, isolation, and sharingof devices.
* Terminals* Disk Drives* Printers* Networks* Keyboard* etc
Device DriversDevice DriversDevice DriversDevice Drivers
Device Independent Part
Application Programming Interface
Device Driver Interface
VendorSpecific
Part
VendorSpecific
Part
VendorSpecific
Part
Process & Resource Process & Resource ManagementManagement
Process & Resource Process & Resource ManagementManagement
Schedules the processor so that each thread/process receivesan equitable fraction of the available time, and maintainsthe execution context for each thread (stack, registers, etc)
Allocates resources to processes when they are requestedand keeps track of resources when a thread is finished withthem. Isolates access to resources or allows sharing ofresources as required.
Memory ManagementMemory ManagementMemory ManagementMemory Management
Maintains a unique address space in memory for eachprocess.
Works with the file and/or device managers to providevirtual memory (address space is larger than physicalmemory).
File ManagementFile ManagementFile ManagementFile Management
Works with the device managers to give applicationsA logical view of storage (byte stream, indexed data,text files, etc), and manage the flow of information between the actual storage device and the program.
Design IssuesDesign IssuesDesign IssuesDesign IssuesPerformance: The OS must be as efficient as possible,maximizing the use of machine resources by applications.There is some overhead involved in providing OS services.If the overhead gets too large, it negates the value ofthe service.
Exclusive Use of Resources: Each process must have theability to have exclusive use of the system resources that it uses. A process must not be able to use a resourceunless the OS has given it permission. Sharing of resourcesshould also be allowed.
* Protection Mechanisms* Security Policies
Processor ModesProcessor ModesProcessor ModesProcessor ModesModern computing hardware provides multiple modes ofoperation:
• User Mode - Cannot execute all machine instructions (e.g. I/O) - Can only access memory allocated to the process
• Privileged Mode - Executes any instruction in the repertoire - Can access protected memory - Only executes trusted software (The OS kernel)
Trap InstructionsTrap InstructionsTrap InstructionsTrap InstructionsUser Space
UserProcess
LibraryCode
. . .fork( );. . .
fork( ){ … trap SYS_FORK( ) . . .}
Kernel
trap table
SYS_FORK
sys_fork( ){ /* system function */ . . . return;}Expensive!
OS OrganizationOS OrganizationOS OrganizationOS Organization
Monolithic Kernels * All OS function resides in the kernel * Fast * difficult to maintain
MicroKernels * The trusted OS software is as small as possible - only the essential OS functions * All other code is implemented in user space * Performance the major issue – many kernel calls required
The first king is very reclusive and sits in a small castle with high walls and a few top advisors. The king tells the advisors what to do and they go outside of the small (but well defended) castle and issue orders to the knights, merchants and common-folk. The king never leaves his castle and since only his most trusted advisors are allowed in the king is very safe from attack. However, because each advisor has to pass through several guard points it can sometimes take a little while before the king’s orders can go out or news can come in.
The second king is much different. He doesn’t really live in a castle so much as it is a large mansion with beautiful grounds. Strongly defended walls encompass the entire city instead of just the castle. This makes the king and the populace very secure from outside attacks. And since this king is very friendly he goes throughout his city meeting and talking with all of his subjects. Any command he, or his many trusted aides, give are instantly obeyed. This makes his city very efficient. However, should any enemy agents manage to penetrate the outer walls, then they can quite easily assassinate the beloved king. In which case order breaks down and the entire city riots.
The Unix KernelThe Unix KernelThe Unix KernelThe Unix Kernel
Trap Table
Monolithic Kernel Module• Process Mgt• Memory Mgt• File Mgt• Device MgtD
river
Inte
rface
Device Driver
Device Driver
OS System Call Interface
Libraries Utilities Apps Shell