Transcript Chapter 1 - OS Overview

Chapter 11 System Management
CIS106
Microcomputer Operating Systems
Gina Rue
CIS Faculty
Ivy Tech State College Northwest Region 01
Introduction System Management
• Four parts of the OS
– Memory Manager
– Processor Manager
– Device Manager
– File Manager
• Each part of the OS depends on the
other parts
See Illustration p.245
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Introduction - System Management
• OS parts work together
• System designer has to consider tradeoffs to improve the system’s efficiency
– improve performance of one component
– cost of that improvement
– how it might affect the performance of the
remainder of the system
• Some methods are used to monitor &
measure system performance,
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accounting & security
Evaluating an OS
• Every OS is different
• Most were originally designed to work
with certain hardware or category of
computer, and to meet specific goals of
the users
– computing environments, multiple systems
– casual users, programmers
– response time, throughput
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Evaluating an OS
• To evaluate an OS, we need to
understand
– design goals
– history
– how it communicates with users
– how resources are managed
– what trade-offs were made to achieve goals
• Need to balance its strengths against its
weaknesses
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OS Four Components
• Improvements in a system can only be
made after extensive analysis of the
needs of the system’s managers & users
• Making one change, you may be trading
one set of problems for another
• Key to consider the performance of the
entire system and not just individual
components
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OS Four Components
• Memory Management
– if you increase memory or change another
memory allocation scheme, you must
consider the actual operating environment
– there is a trade-off between memory use and
CPU overhead
– as memory management algorithms grow
more complex, the CPU overhead increases
and overall performance can suffer
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OS Four Components
• Processor Management
– Let’s say you decide to implement a
multiprogramming system to increase your
processor’s utilization
– multiprogramming requires a great deal of
synchronization between the memory and
processor managers and I/O devices
– The trade-off: better use of the CPU vs.
increased overhead, slower response time, &
decreased throughput
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OS Four Components
• Device Management
– Several ways to improve I/O device utilization
• Blocking reduces the number of physical I/O
requests
• Buffering helps the CPU match the slower speed
of I/O devices
• Rescheduling I/O requests can help optimize I/O
times
–These are trade-offs: each of these
options also increases CPU overhead and
uses additional memory space
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OS Four Components
• File Management
– looks at how secondary storage allocation
schemes help the user organize and access
files on the system
– affects overall system performance
– closely related to the device on which the
files are stored
– different schemes offer different flexibility,
but trade-off for increased file flexibility is
increased CPU overhead
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Measuring System Performance
• Total System Performance - “the
efficiency with which a computer system
meets its goals” - how well it serves it
users
• A system’s efficiency is affected by 3
major components:
– the user’s programs
– operating system programs
– hardware units
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Measuring System Performance
• Measurement Tools
– throughput
– capacity
– response time
– turnaround time
– resource utilization
– availability: MTBF & MTTR
– reliability
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Measuring System Performance
• Feedback loops
– to prevent the processor from spending
more time doing overhead then executing
jobs, the OS must continuously monitor the
system and feed this information to the Job
Scheduler
– negative feedback loop
when system becomes too congested, signals
the appropriate manager to slow down the
arrival of the processes
– positive feedback loop
when the system becomes
13 underutilized,
causes the arrival rate to increase
Measuring System Performance
• Monitoring
– System measurements must include
hardware units, OS, compilers, and other
system software
– Benchmarks are used to objectively measure
and evaluate a system’s performance by
running a set of jobs representative of work
normally done by the system
– Benchmarks are useful when comparing
systems that gone through extensive
changes or by vendors to demonstrate
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advantages of new system
components
Accounting
• Accounting functions - pay the bills and
keeps the system financially operable
• Multi-user environment, the OS must be
able to:
– set up user accounts
– assign passwords
– identify resources available to each user
– define quotas for available resources
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Accounting
• Pricing policies measurements
– total amount of time
– CPU time
– main memory usage
– secondary storage used during program
execution or during billing period
– use of system software
– number of I/O operations & time spent waiting
for I/O completion
– Number of input records read, number of output
records printed
– number of page faults
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Accounting
Maintaining billing records on-line
• Advantage
– status of each user can be checked before
the user’s job is allowed to enter the READY
queue
• Disadvantage
– overhead, an accounting program is kept
active, memory space is used and CPU
processing is increased
– one compromise is to defer the accounting
program until off-hours 17
Ethics
• Cannot be ignored by users or system
administrators
• Organizations should have published
policies clearly stating which actions will
or will not be condoned
– individual needs for privacy
– organization’s need to protect proprietary
information
– public’s right to know as illustrated in
freedom of information laws
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Ethics
• Ethical lapses by authorized or
unauthorized users can have severe
consequences
– illegally copied software
– plagiarism
– eavesdropping on email
– hacking
– unethical use of technology
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System Security
– The system has conflicting needs:
• to share resources
• to protect resources
– With the advent of data communication,
networking, modern telecommunications
software, computer security has become
much more difficult
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System Security
– System Vulnerabilities
• accidental incomplete modification of
data
• data values are incorrectly encoded
• intentional unauthorized access
• wire tapping
• repeated trials
• trash collection
• trap doors
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System Security
– System Assaults: Computer Viruses
• A virus is any unauthorized program
that is designed to:
– gain access to a computer system
– lodge itself in a secretive way by
incorporating itself into other legitimate
programs
– replace itself
• viruses need other programs to spread
– worm
– Trojan horse
– logic bomb
– “pirated” software
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System Security
– System Assaults: Computer Viruses
• Software to combat viruses can be
purchased to protect against viruses
• most extreme protection for sensitive
data is encryption
– putting data into secret code
• disadvantages to encryption
– increase the system’s overhead
– the system becomes totally dependent on
the encryption process itself
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System Security
– Managing Systems
• most systems use a combination of
several protection devices
– passwords
– backups
– maintenance of written security
policies
– training users in proper data
management
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Summary
• OS is the orchestrated cooperation of
every piece of hardware and software
• Trade-offs must be made for optimal
performance
• Appropriate measurement tools and
techniques are used to verify
effectiveness of the system before &
after modifications & then evaluate
degree of improvement
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Summary
• Important to keep system secure
• System is only as good as the integrity of
the data that’s stored on it
• Prevention is the best form of system
security
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