Transcript PPT Chapter 01

Chapter 1
Introduction
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Introduction
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Abstract Views of an Operating System
Goals of an OS
Operation of an OS
Preview of the Book
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Abstract Views of an Operating
System
• What is an OS?
– Abstract views
• To a college student: SW that permits access to the Internet
• To a programmer: SW that makes it possible to develop
programs on a computer system
• To a user of an application package: SW that makes it
possible to use the package
• To a technician in a computerized chemical plant: invisible
component of a computer system that controls the plant
– An abstract view focuses only on essential characteristics
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Abstract Views of an Operating
System (continued)
• Operating system designer also has an abstract view
• OS is a collection of routines that facilitates execution
of user programs and use of resources
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Abstract views
• We use abstract views to present design of OS
components. It has two benefits:
– Managing complexity
• Abstract view contains only selected features of a system
– Presenting a generic view
• For example, user interface of Figure 1.2 has many variants
in practice
– Command line interface
– Graphical user interface (GUI)
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Goals of an OS
• Fundamental goals of an operating system
– Efficient use of computer resources
– User convenience
– Noninterference in the activities of its users
• When these goals conflict, designer makes a trade-off
for
– Efficient use
– User convenience
• Notion of effective utilization
– Each OS provides a different flavor of effectiveness
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Efficient Use
• OS ensures efficient use of memory, CPU, and I/O
devices
– Poor efficiency can result if a program does not use a
resource allocated to it
• OS itself consumes CPU and memory resources, which
constitutes overhead
– It reduces resources for user programs
• OS can monitor use of resources to ensure efficiency
– It would increase the overhead
• OS uses policies that ensure efficiency
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User Convenience
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Noninterference
• User can face interference in computational activities
– Program execution or operation of OS can be disrupted
by actions of other persons
• OS prevents interference by allocating resources for
exclusive use of programs and OS services, and preventing
illegal accesses to resources
– Illegal file access
• OS knows which user files can be accessed by whom
– Achieved through authorization
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Operation of an OS
• Principal functions of OS:
– Program management
– Resource management
– Security and protection
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Operation of an OS (continued)
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Program Management
• OS can interleave execution of programs on a fast CPU
– Scheduling decides which program should be given the
CPU at any time
• Policy influences efficient CPU use and user service
• Preemption: Taking away the CPU from a program
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Resource Management
• Resource allocations and deallocations can be done
with a resource table
– Entry: name, address and status of a resource unit
– Constructed by the boot procedure, maintained during
operation
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Resource Management (continued)
• Popular resource allocation strategies:
– Resource partitioning
• OS decides a priori what resources to allocate to each user
program; divides system resources into partitions
– A resource partition is a collection of resources
• Resource table contains entries for partitions
• Simple to implement, but lacks flexibility
– Pool-based
• OS allocates resources from a pool of resources
– Consults table and allocates the resource if it is free
• Less overhead of allocating and deallocating resources
• Achieves more efficient use of resources
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Resource Management (continued)
• A virtual resource is a fictitious resource
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Abstract view of a resource taken by a program
Supported by OS through use of a real resource
Same real resource may support several virtual ones
Started with the use of virtual devices
• E.g., a print server
• Provides effect of having more resources
• Most OSs provide virtual memory
– May execute a program bigger than size of RAM
• Some OSs create virtual machines
– Each virtual machine can be allocated to a user
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Security and Protection
• Security counters threats of interference or illegal use
posed by persons/programs outside OS control
– Authentication: only registered user can use a computer
system
• Protection counters threats posed by users of an OS
– Memory protection is a HW feature used by OS to thwart
disruption of programs and OS services
– Authorization thwarts interference with files
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Security and Protection (continued)
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Security and Protection (continued)
• Intruders are outsiders who can cause interference
– May use or create malicious programs
• Trojan horses
• Viruses
• Worms
• Methods of addressing security threats
– Authentication techniques
– Plugging security holes
– Internet firewalls
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Preview of the Book
• The book discusses:
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Part 1: Introduction to Operating Systems
Part 2: Managing User Computations
Part 3: Management of Memory
Part 4: Management of Files and I/O Devices
Part 5: Distributed Operating Systems
• Parts 1-4 discuss conventional computing environments
– Single computer system having a single CPU
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Introduction to Operating Systems
• Part 1 (Chapters 1–4)
– How OS interacts with the computer and with user
programs through events and interrupts (Chapter 2)
• See Figure 1.5
– Effective Utilization of a Computer System (Chapter 3)
• Techniques used to ensure effective utilization
– Portability and Extensibility of Operating Systems (Chapter
4)
• Structuring of an OS achieve these goals
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Introduction to Operating Systems
(continued)
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Managing User Computations
• Part 2 (Chapters 5–10) covers program management
– Processes and Threads (Chapter 5)
• How programs are executed
– Process Synchronization (Chapter 6)
• See Figure 1.6
– Scheduling (Chapter 7)
• How to achieve effective utilization
– Deadlocks (Chapter 8)
• See Figure 1.7
– Message Passing (Chapter 9)
– Multiprocessor OSs (Chapter 10)
• Exploiting multiple CPUs for effectiveness
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Managing User Computations
(continued)
• Processes Credit and Debit must access the balance
in an account without interference
• Process Generate produces some data; Analyze uses it
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Managing User Computations
(continued)
• A process has to wait if a required resource is not
available
• Deadlocks arise when processes wait for each other’s
resources
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Management of Memory
• Part 3 (Chapters 11-12) covers memory management
– Memory reuse techniques and noncontiguous memory
allocation (Chapter 11) and virtual memory (Chapter 12)
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Management of Files and I/O Devices
• Part 4 (Chapters 13-15) discusses management of files
and I/O devices
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Management of Files and I/O Devices
(continued)
• Part 4 (Chapters 13-15) (Contd.)
– File Systems (Chapter 13)
• Allows users to create, use, and share files
– Implementation of File Operations (Chapter 14)
• IOCS implements file operations by transferring data
between memory and I/O devices
– Security and Protection (Chapter 15)
• Techniques of thwarting security and protection threats
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Distributed Operating Systems
• Part 5 (Chapters 16-21) discusses distributed OSs:
– Distributed Operating Systems (Chapter 16)
• Model of a distributed computer system
• Networking HW and SW
• Distributed computation paradigms
– Theoretical Issues in Distributed Systems (Chapter 17)
• Theoretical issues that arise from networking delays
and how to tackle them
– Distributed Control Algorithms (Chapter 18)
• Algorithms for performing OS functions in a distributed
manner
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Distributed Operating Systems
(continued)
• Part 5 (Chapters 16-21) (continued):
– Recovery and Fault Tolerance (Chapter 19)
• Issues in recovery and fault tolerance in distributed systems
– Distributed File Systems (Chapter 20)
• Reliability and performance improvement techniques used
in distributed file systems
– Distributed System Security (Chapter 21)
• Techniques used to address security issues in distributed
systems
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Summary
• OS services programs simultaneously by allocating
some of the resources to each program and
interleaving their execution on the CPU
– Requirements to ensure effectiveness of computing:
• Efficient use
• User convenience
• Non-interference
– Primary functions
• Management of programs
• Management of resources
• Security and protection
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