Слайд 2Chapter Goals
Describe the two main responsibilities of an operating system
Define
memory and process management
Explain how timesharing creates the virtual machine
illusion
Explain the relationship between logical and physical addresses
Compare and contrast memory management techniques
Слайд 3Software Categories
Application software Software written to address specific needs—to
solve problems in the real world
Word processing programs, games, inventory
control systems, automobile diagnostic programs,
and missile guidance programs are all application software
System software Software that manages a computer system at a fundamental level
It provides the tools and an environment in which application software can be created and run
Слайд 4Operating System
An operating system
manages computer resources, such as memory
and input/output devices
provides an interface through which a human can
interact with the computer
allows an application program to interact with these other system resources
Слайд 5Operating System
Figure 3.1
An operating system interacts with many
aspects
of a computer system.
Слайд 6Operating System
The various roles of an operating system generally revolve
around the idea of “sharing nicely”
An operating system manages
resources, and these resources are often shared in one way or another among programs that want to use them
Слайд 7Resource Management
Multiprogramming The technique of keeping multiple programs in main
memory at the same time that compete for access to
the CPU so that they can execute
Memory management The process of keeping track of what programs are in memory and where in memory they reside
Слайд 8Resource Management
Process A program in execution
The operating system performs
process management to carefully track the progress of a process
and all of its intermediate states
CPU scheduling determines which process in memory is executed by the CPU at any given point
Слайд 9Batch Processing
A typical computer in the 1960s and ‘70s was
a large machine
Its processing was managed by a human operator
The
operator would organize various jobs from multiple users into batches
Слайд 10Batch Processing
Figure 3.2 In early systems, human operators would organize
jobs into batches
Слайд 11Timesharing
Timesharing system A system that allows multiple users to interact
with a computer at the same time
Multiprogramming A technique that
allows multiple processes to be active at once, allowing programmers to interact with the computer system directly, while still sharing its resources
In a timesharing system, each user has his or her own virtual machine, in which all system resources are (in effect) available for use
Слайд 12Other Factors
Real-time System A system in which response time is
crucial given the nature of the application
Response time The time
delay between receiving a stimulus and producing a response
Device driver A small program that “knows” the way a particular device expects to receive and deliver information.
Слайд 13Memory Management
Operating systems must employ techniques to
Track where and how
a program resides in memory
Convert logical addresses into actual addresses
Logical
address (sometimes called a virtual or relative address) A value that specifies a generic location, relative to the program but not to the reality of main memory
Physical address An actual address in the main memory device
Слайд 14Memory Management
Figure 3.3
Memory is a continuous set of bits
referenced by specific addresses
Слайд 15Single Contiguous Memory Management
There are only two programs in memory
The
operating system
The application program
This approach is called single contiguous
memory management
Figure 3.4
Main memory divided into two sections
Слайд 16Single Contiguous Memory Management
A logical address is simply an integer
value relative to the starting point of the program
To produce
a physical address, we add a logical address to the starting address of the program in physical main memory
Слайд 17Single Contiguous Memory Management
Figure 3.5
binding a logical address to
a physical one
Слайд 18Partition Memory Management
Fixed partitions Main memory is divided into a
particular number of partitions
Dynamic partitions Partitions are created to fit
the needs of the programs
Слайд 19Partition Memory Management
At any point in time memory is divided
into a set of partitions, some empty and some allocated
to programs
Base register A register that holds the beginning address of the current partition
Bounds register A register that holds the length of the current partition
Figure 3.6
Address resolution
in partition memory management
Слайд 20Partition Selection Algorithms
Which partition should we allocate to a new
program?
First fit Allocate program to the first partition big
enough to hold it
Best fit Allocated program to the smallest partition big enough to hold it
Worst fit Allocate program to the largest partition big enough to hold it
Слайд 21Paged Memory Management
Paged memory technique A memory management technique in
which processes are divided into fixed-size pages and stored in
memory frames when loaded into memory
Frame A fixed-size portion of main memory that holds a process page
Page A fixed-size portion of a process that is stored into a memory frame
Page-map table (PMT) A table used by the operating system to keep track of page/frame relationships
Слайд 22Paged Memory Management
To produce a physical address, you first look
up the page in the PMT to find the frame
number in which it is stored
Then multiply the frame number by the frame size and add the offset to get the physical address
Figure 3.7
A paged memory management approach
Слайд 23Paged Memory Management
Demand paging An important extension of paged memory
management
Not all parts of a program actually have to be
in memory at the same time
In demand paging, the pages are brought into memory on demand
Page swap The act of bringing in a page from secondary memory, which often causes another page to be written back to secondary memory
Слайд 24Paged Memory Management
The demand paging approach gives rise to the
idea of virtual memory, the illusion that there are no
restrictions on the size of a program
Too much page swapping, however, is called thrashing and can seriously degrade system performance.
Слайд 25Have A Good Night
Autumn Moon
by Ansel Adams
Nasa Encore
