问题 问答题

某请求分页系统的局部页面置换策略如下:
系统从0时刻开始扫描,每隔36个时间滴答扫描一轮工作集(扫描时间忽略不计),本轮没有被访问过的页框将被系统回收,并放入到空闲页框链尾,其中内容在下一次被分配之前不被清空。当发生缺页时,如果该页曾被使用过且还在空闲页框链表中,则重新放回进程的工作集中;否则,从空闲页框链表头部取出一个页框进行分配。
假设不考虑其他进程的影响和系统开销,初始时进程工作集为空。目前系统空闲页框链表中页框号依次为198、156、188、230。进程P依次访问的<虚拟页号,访问时刻>是:<1,1>、<3,20>、<0,32>、<0,65>、<1,73>、<0,90>、<2,104>。请回答下列问题。

访问<1,73>时,对应的页框号是什么,说明理由;

答案

参考答案:页框号为198。理由:因73>(36×2)故发生第二轮扫描,页号为1、3的页框198、156在第二轮已处于空闲页框链表中,此刻1页又被重新访问,因此应被重新放回到工作集中。其页框号为198。

阅读理解

Fat and shy, Ben Saunders was the last kid in his class picked for any sports team. “Football, tennis, cricket - anything with a round ball, I was useless,” he says now with a laugh. But back then he was the one always made fun of in school gym classes in Devonshire, England.

It was a mountain bike he received for his 15th birthday that changed him. At first he went biking alone in a nearby forest. Then he began to ride the bike along with a runner friend. Gradually, Saunders set up his mind on building up his body, increasing his speed and strength. At the age of 18, he ran his first marathon.

The following year he met John Ridgway and started to work as an instructor at Ridgway’s school of adventure(冒险) in Scotland, where he learnt about Ridgway’s cold-water exploits. Greatly interested, Saunders read all he could about North Pole explorers and adventures, he decided that this would be his future.

In 2001, after becoming a skillful skier, Saunders started his first long-distance expedition (探险)towards the North Pole. It took unbelievable energy. He suffered frostbite(冻伤), ran into a polar bear and pushed his body to the limit, pulling his sled up and over the rocky mountains.

Saunders has since become the youngest person to ski alone to the North Pole, and he’s skied more of the North Pole by himself than any other British man. His old playmates would not believe the change.

小题1: What changed Saunders according to Paragraph 2?

A.A friend’s words.

B.A mountain bike.

C.His 18th birthday gift.

D.His first marathon.小题2:What did Saunders do in 2001?

A.He decided to build up his body.

B.He met John Ridgway in Scotland.

C.He worked as an instructor at school.

D.He took an adventure to the North Pole.小题3:What does the story mainly tell us about Saunders?

A.He is a success in sports.

B.He is the youngest British skier.

C.He is Ridgway’s best student.

D.He is a good instructor at school.

单项选择题