问答题

数据存储在磁盘上的排列方式会影响I/O服务的总时间。假设每磁道划分成10个物理块,每块存放1个逻辑记录。逻辑记录R1,R2,…,R10存放在同一个磁道上,记录的安排顺序如下表所示:

假定磁盘的旋转速度为20ms/周,磁头当前处在R1的开始处。若系统顺序处理这些记录,使用单缓冲区,每个记录处理时间为4ms,则处理这10个记录的最长时间为(15);若对信息存储进行优化分布后,处理10个记录的最少时间为(16)。
A.180ms
B.200ms
C.204ms
D.220ms

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假定磁盘的旋转速度为20ms/周,磁头当前处在R1的开始处。若系统顺序处理这些记录,使用单缓冲区,每个记录处理时间为4ms,则处理这10个记录的最长时间为(15);若对信息存储进行优化分布后,处理10个记录的最少时间为(16)。
A.180ms
B.200ms
C.204ms
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【案例分析题】

After lunch,without their parents’【C1】______,the two boys set off’to explore the beach which beyond the headland(岬).They had【C2】______their young sister to【C3】______,saying that the long【C4】______would be too【C5】______for her.Once they had got beyond the headland,the beach stretched(延伸)away endlessly before them.It was like【C6】______a new world.Here and【C7】______along the beach there were lots of sea -creatures.The two boys kept searching everywhere for those【C8】______things.
The afternoon passed【C9】______.The sun was already【C10】______when the boys reluctantly【C11】______to make their way homewards.But long before they reached the headland,they could【C12】______that the tide had come in so far that they were now【C13】______from either end of the beach.Their only【C14】______of returning back was to find a way up the cliff(悬崖)nearby.
They soon found a narrow path【C15】______to the cliff top.But halfway up,their only【C16】______was blocked by a【C17】______rock which they could not climb【C18】______.The two boys had to shout at the top of their voice,【C19】______that someone【C20】______come to help them out.Just then,to their great surprise,their father appeared over the top of the rock,and with him were two policemen.One of them climbed down with a rope which was lowered over the rock.The two boys were then pulled up to safety and thus saved from spending a miserable night on the cliff.

【C1】()

A.promise
B.permission
C.suggestion
D.advice

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