【文章內(nèi)容簡介】 er as a group by an operator or automatic job sequencer. Performance is increased by attempting to keep CPU and I/O devices busy at all times through buffering, offline operation, spooling, andmultiprogramming. Batch is good for executing large jobs that need little interaction。 it can be submitted and picked up later.b. Interactive. This system is posed of many short transactions where the results of the next transaction may be unpredictable. Response time needs to be short (seconds) since the user submits and waits for the result.c. Time sharing. This systems uses CPU scheduling and multiprogramming to provide economical interactive use of a system. The CPU switches rapidly from one user to another. Instead of having a job defined by spooled card images, each program reads its next control card from the terminal, and output is normally printed immediately to the screen.d. Real time. Often used in a dedicated application, this system reads information from sensors and must respond within a fixed amount of time to ensure correct performance.e. Network. Provides operating system features across a network such as file sharing.f. SMP. Used in systems where there are multiple CPU’s each running the same copy of the operating takes place across the system bus.g. system distributes putation among several physical processors. The processors do not share memory or a clock. Instead, each processor has its own local memory. They municate with each other through various munication lines, such as a highspeed bus or local area network.h. Clustered. A clustered system bines multiple puters into a single system to perform putational task distributed across the cluster.i. Handheld. A small puter system that performs simple tasks such as calendars, , and web browsing. Handheld systems differ from traditional desktop systemswith smallermemory and display screens and slower processors. What are the tradeoffs inherent in handheld puters?Answer: Handheld puters are much smaller than traditional desktop PC’s. This results in smaller memory, smaller screens, and slower processing capabilities than a standard desktop PC. Because of these limitations,most handhelds currently can perform only basic tasks such as calendars, , and simple word processing. However, due to their small size, they are quite portable and, when they are equipped with wireless access, can provide remote access to electronic mail and the world wide web.Chapter 2 The services and functions provided by an operating system can be divided into two main categories. Briefly describe the two categories and discuss how they differ.Answer: One class of services provided by an operating system is to enforce protection between different processes running concurrently in the system. Processes are allowed to access only thosememory locations that are associated with their address spaces. Also, processes are not allowed to corrupt files associated with other users. A process is also not allowed to access devices directly without operating system ntervention.The second class of services provided by an operating system is to provide new functionality that is not supported directly by the underlying hardware. Virtual memory and file systems are two such examples of new services provided by an operating system. List five services provided by an operating system that are designed to make it more convenient for users to use the puter system. In what cases it would be impossible for userlevel programs to provide these services? Explain.Answer: ? Program execution. The operating system loads the contents (or sections) of a file into memory and begins its execution. A userlevel program could not be trusted to properly allocate CPU time.? I/O operations. Disks, tapes, serial lines, and other devices must be municated with at a very low level. The user need only specify the device and the operation to perform on it, while the system converts that request into device or controllerspecific mands. Userlevel programs cannot be trusted to only access devices they should have access to and to only access them when they are otherwise unused.? Filesystem manipulation. There are many details in file creation, deletion, allocation, and naming that users should not have to perform. Blocks of disk space are used by files and must be tracked. Deleting a file requires removing the name file information and freeing the allocated blocks. Protections must also be checked to assure proper file access. User programs could neither ensure adherence to protection methods nor be trusted to allocate only free blocks and deallocate blocks on file deletion.? Communications. Message passing between systems requires messages be turned into packets of information, sent to the network controller,transmitted across a munications medium, and reassembled by the destination system. Packet ordering and data correction must take place. Again, user programs might not coordinate access to the network device, or they might receive packets destined for other processes.? Error detection. Error detection occurs at both the hardware and software levels. At the hardware level, all data transfers must be inspected to ensure that data have not been corrupted in transit. All data on media must be checked to be sure they have not changed since they were written to the media. At the software level, media must be checked for data consistency。 for instance, do the number of allocated and
unallocated blocks of storage match the total number on the device. There, errors are frequently processindependent (for instance, the corruption of data on a disk), so there must be a global program (the operating system) that handles all types of errors. Also, by having errors processed by the operating system, processes need not contain code to catch and correct all the errors possible on a system. Describe three general methods for pas