1. In a multiprogramming and time-sharing environment, several users share the s
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Question
1. In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. a. What are two such problems? b. Can we ensure the same degree of security in a time-shared machine as in a dedicated machine? Explain your answer.
2. The issue of resource utilization shows up in different forms in different types of operating systems. List what resources must be managed carefully in the following settings: a. Mainframe or minicomputer systems b. Workstations connected to servers c. Mobile computers
3. Under what circumstances would a user be better off using a time-sharing system than a PC or a single-user workstation?
4. Describe the differences between symmetric and asymmetric multiprocessing. What are three advantages and one disadvantage of multiprocessor systems?
5. How do clustered systems differ from multiprocessor systems? What is required for two machines belonging to a cluster to cooperate to provide a highly available service?
6. Consider a computing cluster consisting of two nodes running a database. Describe two ways in which the cluster software can manage access to the data on the disk. Discuss the benefits and disadvantages of each.
7. How are network computers different from traditional personal computers? Describe some usage scenarios in which it is advantageous to use network computers.
8. What is the purpose of interrupts? How does an interrupt differ from a trap? Can traps be generated intentionally by a user program? If so, for what purpose?
9. Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU’s execution load. a. How does the CPU interface with the device to coordinate the transfer? b. How does the CPU know when the memory operations are complete? c. The CPU is allowed to execute other programs while the DMA controller is transferring data. Does this process interfere with the execution of the user programs? If so, describe what forms of interference are caused.
10. Some computer systems do not provide a privileged mode of operation in hardware. Is it possible to construct a secure operating system for these computer systems? Give arguments both that it is and that it is not possible.
11. Many SMP systems have different levels of caches; one level is local to each processing core, and another level is shared among all processing cores. Why are caching systems designed this way?
12. Discuss, with examples, how the problem of maintaining coherency of cached data manifests itself in the following processing environments: a. Single-processor systems b. Multiprocessor systems c. Distributed systems
Explanation / Answer
b. Yes, if we can ensure that the OS (operating system) prevents any sharing of data between users, either for reading or writing, and fairly shares the computer, then we can achieve the same level of security
2) a. Resources that must be managed carefully for Mainframes systems are memory and CPU resources, storage, and network bandwidth
b. Resources that must be managed carefully for Workstations are memory and CPU resources
c. Resources that must be managed carefully for Handheld computers are power consumption and memory resources
3) A user is better off using a time sharing system under three situations: when it is Low in price, Rapid, and easier. For example:
i. When the user is paying for management costs, and the costs are cheaper for a time-sharing system than for a single-user computer.
ii. When running a large task that takes more time to run on a single PC or workstation.
iii. When a user is at different location and doesn't have laptop to carry around, they can connect remotely to a time-shared system and do their work.
4). Symmetric multiprocessing treats all processors as equals, and I/O can be processed on any CPU.
Asymmetric multiprocessing has one master CPU and the remaining CPUs are slaves. The master distributes tasks among the slaves, and I/O is usually done by the master only.
The advantages of multiprocessor are
i. Reduced Cost: Multiple processors share the same resources like power supply or mother board for each chip is not required. This reduces the cost.
ii. Increased Reliability: The reliability of system is also increased. The failure of one processor does not affect the other processors though it will slow down the machine. Several mechanisms are required to achieve increased reliability. If a processor fails, a job running on that processor also fails. The system must be able to reschedule the failed job or it will alert the user that the job was not successfully completed.
iii. Increased Throughput: An increase in the number of processes completes the work in less time.
The main disadvantage of multiprocessor system
i. If one processor fails then it will affect in the speed
ii. Multiprocessor systems are expensive and complex hardware and software and large memory is required
5. Clustered systems are ordinarily constructed by consolidating numerous PCs into a solitary system to play out a computational task distribution over the cluster .multiprocessor system then again could be a solitary physical substance containing numerous CPUs. A Clustered system is less firmly coupled than a multiprocessor system .Clustered system convey utilizing messages, while processors in a multiprocessor system communicate utilizing shared memory
In order for two machines to provide a highly available service, the state on the two machines should to be duplicated and should to be reliably refreshed. When one of the machines comes up short, then other could take over the usefulness of the fizzled machine
6. Consider the following two alternatives: asymmetric clustering and parallel clustering
With asymmetric clustering, one host runs the database application with the other host basically checking it. In the event that the server fails, the checking host turns into the active server. This is appropriate for providing redundancy. However it does not utilize the potential processing power of both hosts
With parallel clustering, the database application can keep running in parallel on the two hosts. The trouble in executing parallel clustering is giving some type of conveyed bolting system for records on the shared disk
7. Personal Computers are more secure and are anything but difficult to settle when they break, however a system Personal Computers is a terminal that speaks with different terminals by means of the web (TCP/IP being the most widely recognized system convention). A networking protocol needs an interface gadget with a gadget driver and programming to deal with information, so to the operating system this is somewhat negligible. Further, the information is generally centralized, so Computers associated with the system are largely ready to get a similar data without saving it onto their system or send it to another system. At the point when there will be sharing, a network computers is smarter to use than a Personal Computers
8. An interrupt is a hardware-generated change-of flow within the system. An interrupt handler is summoned to deal with the cause of the interrupt; control is then returned to the interrupted context and instruction.A trap is a softwaregenerated interrupt. An interrupt can be used to signal the completion of an I/O to obviate the need for device polling. A trap can be used to call operating system routines or to catch arithmetic errors.
9. The CPU can start a Direct Memory Access operation by composing esteems into extraordinary registers that can be freely accessed by the device. The device starts the comparing operation once it gets an order from the CPU. At the point when the device is done with its operation, it intruded on the CPU to show the culmination of the operation. Both the device and the CPU can be getting to memory all the while. The memory controller gives access to the memory transport in a reasonable way to these two entities. A CPU may along these lines be unable to issue memory operations at crest speeds since it needs to finish with the device to get access to the memory bus
10. It IS possible:
The computer would have to be constantly observing.
It IS NOT possible:
Privileged mode is used to start up the operating system. It must switch to user mode, after which time a user program can take control of the system. Certain privileged instructions can only be done in privileged mode as well. This protects the operating system from users and protects users from each other’s. Removing the privileged mode makes the system less secure and likely to be destroyed by errant users.
11 In single-processor System, the memory should be refreshed when a processor issues updates to stored esteems. These updates can be performed quickly or in a languid way. In a multiprocessor System, distinctive processors may reserve a similar memory area in its neighborhood stores. At the point when refreshes are made, the other cached locations should be negated or refreshed. In distributed systems, consistency of cached memory esteems isn't an issue. Nonetheless, consistency issues may emerge when a customer stores document information.
12. Any memory location updated by the will first be updated in cache, and later in memory; later depends on the cache
In a single-processor system, this is a consistency problem, not a coherence problem.
In a multiprocessor system, two processors may have stacked a similar incentive from memory, and it would be put in partitioned caches, one for every processor. In the event that one processor refreshes the esteem that ought to be imparted to the next processor, or to the next processor's reserve, contingent upon how you need to plan the caches you could negate the second duplicate in cache, or refresh it. The system transport is included with this operation. In the long run, the memory is refreshed, as in a solitary processor system
In distributed systems, nothing about cache or memory is shared, but the file system might be shared. If so, the same problems arise by caching files in main memory. The network substitutes for the system bus.
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