Chapter 11

Operating Systems

Outline

Functional overview of an operating system Process management Resource allocation

CPU allocation Memory allocation

Interprocess communication

Operating System Overview

Operating System Management Functions Operating System Layers

Operating System Overview The operating system oversees all hardware

resources and allocates them to user and applications as needed.

The operating system performs many low-level tasks on behalf of users and application programs.

Operating System OverviewOperating System Management Functions

The operating system manages: Hardware resources Users and their programs

Operating System OverviewOperating System Layers

Command Layer Service Layer Kernel

Operating System Layers

Operating System Layers

Operating System Layers Command Layer – the user’s interface to the

operating system.

Service Layer – contains a set of functions called by application programs and the command layer.

Kernel – manages resources and directly interacts with computer hardware.

Outline

Functional overview of an operating system Process management Resource allocation

CPU allocation Memory allocation

Interprocess communication

Process Management

Process Control Data Structures

A process is a unit of executing software that is managed independently by the operating system.

A process can request and receive hardware resources and operating system services.

Process Management

Process Control Data Structures

Process Control Block (PCB) – keeps track of each process by creating and updating a data structure.

The PCB is created when the process is created, updated when the process changes and deleted when the process terminates.

Process Management

Data included in a PCB: A unique process identification number The current state of the process Events for which the process is waiting Resources allocated exclusively to the

process Machine resources consumed Process ownership and/or access privileges Scheduling priority

Process Management

Threads A portion of a process that can be scheduled

and executed independently. Process light

Thread can execute concurrently on a single processor or simultaneously on multiple processors.

Outline

Functional overview of an operating system Process management Resource allocation

CPU allocation Memory allocation

Interprocess communication

Resource Allocation

Single Process Resource Allocation Multiple Process Resource Allocation Resource Allocation Processes Real and Virtual Resources

Resource Allocation

Single Process Resource Allocation

Involves only two executing programs – application and operating system.

When an application program begins executing, the operating system grants it control of all unused resources.

Resource Allocation

Single Process Resource Allocation

Most service calls are actually indirect requests for system resources.

MS-DOS is a single-tasking operating system.

Resource Allocation

Multiple Process Resource Allocation

Multitasking operating systems are the norm for general-purpose computers.

Multitasking operating systems must be able to handle multiple programs and users.

Resource Allocation

Multiple Process Resource Allocation

A multitasking operating system manages hardware resources to achieve the following: Meet the resource needs of processes Prevent processes from interfering with one

another Efficiently use hardware and other resources

Resource Allocation

Resource Allocation Processes

Keeps detailed records of available resources. Knows which resource are used to satisfy which

requests. Schedules resources based on specific allocation

policies to meet present and anticipated demands. Updates records to reflect resources commitment

and release by processes and users.

Resource Allocation

Real and Virtual Resources

Real resource – a computer system’s physical devices and associated system software.

Virtual resource – the resources that are apparent to a process or user.

Real and Virtual Resources

Providing virtual resources that meet or exceed resources is accomplished by:

Rapidly shifting resources unused by one process to other processes that need them.

Substituting one type of resource for another when possible and necessary.

CPU Allocation

Thread States Interrupt Processing Scheduling

CPU Allocation

A thread controls the CPU for no more than a few milliseconds before it relinquishes control and the operating system gives another thread a turn.

CPU sharing is called concurrent execution or interleaved execution.

CPU Allocation

CPU Allocation

Thread States

Ready Running Blocked

CPU Allocation

CPU Allocation

Ready State – a thread is waiting for access to a CPU.

Running State – the thread has control of the CPU. The thread or its parent process terminates

normally An interrupt occurs

Block State – the thread is suspended while an interrupt is being processed.

CPU Allocation

Interrupt Processing

A blocked thread is waiting for an event to occur.

If the event is the correction of an error and it can be corrected, the thread remains in the blocked state until the error condition is resolved; otherwise, the thread is halted.

Scheduling

Preemptive Scheduling Priority-based Scheduling Real-time Scheduling

Scheduling

Preemptive Scheduling

A thread can be removed involuntarily from the running state.

A running process controls the CPU by controlling the content of the instruction pointer.

CPU control is lost whenever an interrupt is received.

Scheduling

Scheduling

Scheduling

Priority-Based Scheduling Methods:

First come First served Explicit priority Shortest time remaining

Scheduling

Priority-Based: First come first served:

The scheduler always dispatches the ready thread that has been waiting the longest.

Scheduling

Priority-Based: Explicit priority:

Uses a set of priority levels and assigns a level to each process or thread.

The scheduling method can use priority levels in two ways: Always dispatch the highest priority ready thread Assign larger time slices to high priority threads

Scheduling

Priority-Based: Shortest time remaining:

Chooses the next process to be dispatched based on the expected amount of CPU time needed to complete the process.

Scheduling

Real-Time Scheduling:

Guarantees a minimum amount of CPU time to a thread if the thread makes an explicit request when it is created.

Used when a thread must have enough resources to complete its function within a specified time.

Technology Focus

Windows 2000 Scheduling

Technology Focus

Memory Allocation

Single-Tasking Memory Allocation Multitasking Memory Allocation Memory Fragmentation Noncontiguous Memory Allocation Virtual Memory Management Memory Protection Memory Management Hardware

Memory Allocation

Single-Tasking Memory Allocation – Contiguous Memory Allocation

The bulk of the operating system occupies lower memory addresses.

The application program is loaded above the operating system.

The remaining space is available for user programs and data.

Memory Allocation

Memory Allocation

Single-Tasking Memory Allocation – Noncontiguous Memory Allocation

To conserve physical memory, some operating system components are loaded into memory only when needed.

When loaded, they usually are placed in upper memory.

Memory Allocation

Memory Allocation

Multitasking Memory Allocation

The goals of multitasking memory allocation are: Allow as many active processes as possible. Respond quickly to changing memory demands of

processes. Prevent unauthorized changes to a process’s

memory region(s). Implement memory allocation and addressing as

efficiently as possible.

Memory Allocation

Memory Allocation

Memory Allocation

Memory Allocation

Memory Fragmentation

As processes are created, executed, and terminated, memory allocation changes accordingly.

Memory partition allocation and deallocation leads to an increasing number of small free partitions separated by allocated partitions.

Memory Allocation

Memory Allocation

Memory Allocation

Noncontiguous Memory Allocation

Uses small fixed-size partitions, usually no larger than 64K.

A process can be loaded into more than one partition.

Memory Allocation

Memory Allocation

Virtual Memory Management Divides a program into partitions called

pages. Memory is divided into pages called a page

frame. During program execution, one or more

program pages are stored in a page frame, the remaining are stored on a secondary storage device.

Memory Allocation

Memory Allocation

Memory Protection Refers to the protection of memory allocated

to one program from unauthorized access by another program.

The operating system checks each write to a memory location to ensure that the address being written is allocated to the program performing the write operation.

Memory Allocation

Memory Management Hardware

Modern CPUs and computer systems incorporate advanced memory allocation and address resolution functions in hardware.

Technology Focus

Technology Focus

Outline

Functional overview of an operating system Process management Resource allocation

CPU allocation Memory allocation

Interprocess communication

Interprocess Communication

Interprocess Signals Interprocess Data Communication

Interprocess CommunicationInterprocess Signals

A signal is a message used to synchronize the actions of two processes or threads.

Signals can be sent between threads of the same process, between independent processes, or between the operating system and a process or thread.

Interprocess Communication

Interprocess Communication

Interprocess Communication

Interprocess CommunicationInterprocess Data Communication

Operating systems provide a mechanism called a pipe so there can be communication via shared memory between independent processes.

Interprocess Communication

Interprocess Communication

Summary

An operating system is the most complex component of system software.

The operating system allocates hardware resources to individual user processes on demand.

The operating system stores information about each process in a PCB.

Summary

Application software is simper to develop if programs are unaware of resource allocation functions.

An active thread is always in one of three states – ready, running, or blocked.

Summary

Memory is divided into fixed-size partitions and processes are allocated one or more memory partitions to store instructions and data.

Modern operating systems implement a form of memory allocation and management called virtual memory management.

Summary

Processes and threads often need to synchronize their actions or transfer data among themselves using signals and pipes.