操作系统概念第七版答案Word格式.docx

1、 b. can we ensure the same degree of security in a time-shared machine as in a dedicated machine? explain your answer. answer: a. stealing or copying ones programs or data; using system resources （cpu, memory, disk space, peripherals） without proper accounting. b. probably not, since any protection

2、scheme devised by humans can inevitably be broken by a human, and the more complex the scheme, the more difficult it is to feel confident of its correct implementation. 1.2 the issue of resource utilization shows up in different forms in different types of operating systems. list what resources must

3、 be managed carefully in the following settings: a. mainframe or minicomputer systems b. workstations connected to serversc. handheld computers a. mainframes:memory and cpu resources, storage, network bandwidth. b. workstations: memory and cpu resouces c. handheld computers: power consumption, memor

4、y resources. 1.3 under what circumstances would a user be better off using a timesharing system rather than a pc or single-user workstation? when there are few other users, the task is large, and the hardware is fast, time-sharingmakes sense. the full power of the system can be brought to bear on th

5、e users problem. the problemcan be solved faster than on a personal computer. another case occurs when lots of other users need resources at the same time. a personal computer is best when the job is small enough to be executed reasonably on it and when performance is sufficient to execute the progr

6、am to the users satisfaction. 1.4 which of the functionalities listed below need to be supported by the operating system for the following two settings: （a） handheld devices and （b） real-time systems. a. batch programmingb. virtual memoryc. time sharing for real-time systems, the operating system ne

7、eds to support virtual memoryand time sharing in a fair manner. for handheld systems,the operating system needs to provide virtual memory, but does not need to provide time-sharing. batch programming is not necessary in both settings. 1.5 describe the differences between symmetric and asymmetric mul

8、tiprocessing.what are three advantages and one disadvantage of multiprocessor systems? symmetric multiprocessing treats all processors as equals, and i/o can be processed on any cpu. asymmetric multiprocessing has one master cpu and the remainder cpus are slaves. the master distributes tasks among t

9、he slaves, and i/o is usually done by the master only. multiprocessors can save money by not duplicating power supplies,housings, and peripherals. they can execute programs more quickly and can have increased reliability. they are also more complex in both hardware and software than uniprocessor sys

10、tems. 1.6 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? clustered systems are typically constructed by combining multiple computers into a single system to perform a computatio

11、nal task distributed across the cluster. multiprocessor systems on the other hand could be a single physical entity comprising of multiple cpus. a clustered system is less tightly coupled than a multiprocessor system.clustered systems communicate using messages, while processors in a multiprocessor

12、system could communicate using shared memory. in order for twomachines to provide a highly available service, the state on the two machines should be replicated and should be consistently updated. when one of the machines fail, the other could then take-over the functionality of the failed machine.

13、1.7 distinguish between the client-server and peer-to-peer models of distributed systems. the client-server model firmly distinguishes the roles of the client and server. under this model, the client requests services that are provided by the server. the peer-to-peer model doesnt have such strict ro

14、les. in fact, all nodes in the system are considered peers and thus may act as either clients or servers - or both. a node may request a service from another peer, or the node may in fact provide such a service to other peers in the system. for example, lets consider a system of nodes that share coo

15、king recipes.under the client-server model, all recipes are stored with the server. if a client wishes to access a recipe, it must request the recipe from the specified server. using the peer-to-peer model, a peer node could ask other peer nodes for the specified recipe.the node （or perhaps nodes） w

16、ith the requested recipe could provide it to the requesting node. notice how each peer may act as both a client （i.e. it may request recipes） and as a server （it may provide recipes.） 1.8 consider a computing cluster consisting of twonodes running adatabase.describe two ways in which the cluster sof

17、tware can manage access to the data on the disk. discuss the benefits and disadvantages of each. consider the following two alternatives: asymmetric clustering and parallel clustering. with asymmetric clustering, one host runs the database application with the other host simply monitoring it. if the

18、 server fails, the monitoring host becomes 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 run in parallel on both hosts. the difficulty implementing par

19、allel clusters is providing some form of distributed locking mechanism for files on the shared disk. 1.9 how are network computers different from traditional personal computers? describe some usage scenarios in which it is advantageous to use network computers. a network computer relies on a central

20、ized computer for most of its services. it can therefore have a minimal operating system to manage its resources. a personal computer on the other hand has to be capable of providing all of the required functionality in a standalonemanner without relying on a centralized manner. scenarios where admi

21、nistrative costs are high and where sharing leads to more efficient use of resources are precisely those settings where network computers are preferred. 1.10 what is the purpose of interrupts? what are the differences between a trap and an interrupt? can traps be generated intentionally by a user pr

22、ogram? if so, for what purpose? 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 software-generated interrupt. an interrupt

23、 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. 1.11 direct memory access is used for high-speed i/o devices in order to avoid increasing the cpus execution load. a. how does t

24、he 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 istransferring data. does this process interfere with the execution of the user programs? if so, des

25、cribe what forms of interference are caused. the cpu can initiate a dma operation by writing values into special registers that can be independently accessed by the device.the device initiates the corresponding operation once it receives a command from the cpu. when the device is finished with its o

26、peration, it interrupts the cpu to indicate the completion of the operation. both the device and the cpu can be accessing memory simultaneously.the memory controller provides access to the memory bus in a fair manner to these two entities. a cpu might therefore be unable to issue memory operations a

27、t peak speeds since it has to compete with the device in order to obtain access to the memory bus. an operating system for a machine of this type would need to remain in control （or monitor mode） at all times. this could be accomplished by two methods: a. software interpretation of all user programs

28、 （like some basic,java, and lisp systems, for example）. the software interpreter would provide, in software, what the hardware does not provide. b. require meant that all programs be written in high-level languages so that all object code is compiler-produced. the compiler would generate （either in-

29、line or by function calls） the protection checks that the hardware is missing. 1.13 give two reasons why caches are useful.what problems do they solve? what problems do they cause? if a cache can be made as large as the device for which it is caching （for instance, a cache as large as a disk）, why n

30、ot make it that large and eliminate the device? caches are useful when two or more components need to exchange data, and the components perform transfers at differing speeds.caches solve the transfer problem by providing a buffer of intermediate speed between the components. if the fast device finds

31、 the data it needs in the cache, it need not wait for the slower device. the data in the cache must be kept consistent with the data in the components. if a omponent has a data value change, and the datum is also in the cache, the cache must also be updated. this is especially a problem on multiprocessor systemswhere more than one process may be accessing a datum.acomponent may be eliminated by an equal-sized cache, but only if: （a） the cache and the component have equivalent state-saving capacity （that is,if the component retains its data when elect