Transcript Operating Systems - Cal State LA

Operating Systems
Chapter 11
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Chapter Topics
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Operating System Overview
Operating System Management
Functions:
 Oversees all hardware resources and
allocates them to user and applications
as needed
 Performs many low-level tasks on behalf
of users and application programs
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Operating System Overview
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Operating System Overview
Operating System Layers:
 Command Layer (shell) – 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
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Operating System Overview
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Operating System Overview
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Resource Allocation
Resource Allocation Process:
 Keeps detailed records of available resources
 Knows which resources 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
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Resource Allocation
Single Process Resource Allocation
(application program and operating
system):
 When an application program begins
executing, the operating system grants it
control of all unused resources
 Most service calls are actually indirect
requests for system resources
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Resource Allocation
Multiple Process Resource Allocation:
 Multitasking operating systems are the norm for generalpurpose computers
 Multitasking operating systems must be able to handle
multiple programs and users
 A multitasking operating system manages hardware
resources to achieve the following:
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Meet the resource needs of processes
Prevent processes from interfering with one another
Efficiently use hardware and other resources
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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
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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
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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.
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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
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CPU Allocation
Concurrent Execution (Interleaved
Execution):
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A thread is a portion of a process that can
be scheduled and executed independently.
It controls the CPU for no more than a few
milliseconds before it relinquishes control
and the operating system gives another
thread a turn
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CPU Allocation
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CPU Allocation
1.
2.
3.
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Ready State – a thread is waiting for
access to a CPU
Block State – the thread is suspended
while an interrupt is being processed
Running State – the thread has control
of the CPU.
The thread or its parent process
terminates normally
An interrupt occurs
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CPU Allocation
Scheduling:
Preemptive Scheduling –
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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
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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
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CPU Allocation
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CPU Allocation
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Technology Focus
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CPU Allocation
Priority-Based:
 First-come first served:
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The scheduler always dispatches the ready
thread that has been waiting the longest.
 Explicit priority:
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Uses a set of priority levels and assigns a
level to each process or thread.
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CPU Allocation
Shortest Remaining Time:
Chooses the next process to be
dispatched based on the expected
amount of CPU time needed to complete
the process.
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Technology Focus
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Memory Allocation
 Single-Tasking Memory Allocation
 Multitasking Memory Allocation
 Memory Fragmentation
 Noncontiguous Memory Allocation
 Virtual Memory Management
 Memory Protection
 Memory Management Hardware
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Memory Allocation
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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.
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Memory Allocation
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Memory Allocation
Multitasking Memory Allocation:
 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.
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Memory Allocation
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Memory Allocation
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Memory Allocation
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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
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Memory Allocation
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Memory Allocation
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Memory Allocation
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Memory Allocation
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Technology Focus
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Technology Focus
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Interprocess Communication
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Interprocess Communication
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Interprocess Communication
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Interprocess Communication
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Interprocess Communication
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