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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 2 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, 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 Measuring System Performance • Measurement Tools – throughput – capacity – response time – turnaround time – resource utilization – availability: MTBF & MTTR – reliability 12 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 14 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 15 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 16 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 18 Ethics • Ethical lapses by authorized or unauthorized users can have severe consequences – illegally copied software – plagiarism – eavesdropping on email – hacking – unethical use of technology 19 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 20 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 21 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 22 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 23 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 24 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 25 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 26