问题 单项选择题

假设微处理器的主频为50MHz,两个时钟周期组成一个机器周期,平均三个机器周期完成一条指令,则它的机器周期是 (6) ns,平均运算速度约为 (7) MIPS。

A.2

B.3

C.6

D.8

答案

参考答案:D

解析:试题6~7

[分析]: 计算机主频的周期是指时钟周期,时钟周期表示了SDRAM所能运行的最高频率,更小的时钟周期就意味着更高的工作频率。
CPU周期又称机器周期,是CPU访问一次内存所花的时间,因此用从内存读取一条指令字的最短时间来定义。
题目中告诉我们,两个时钟周期组成一个机器周期,而微处理器的主振频率为 50MHz,即时钟周期=1/50MHz=20ns,由此可以计算出机器周期两倍时钟周期为40ns。
MIPS(每秒百万条指令)是表示机器运算速度的单位,意思是每秒钟所能执行的指令条数。在本题中,由于平均每3个机器周期完成一条指令,而一个机器周期的为40ns,因此,平均执行一条指令需要120ns的时间。也就是说,每秒钟能执行的指令条数为 1/120ns,即8.3×106条指令,也就是8.3MIPS。

完形填空

Of all living creatures on earth, insects are the most plentiful. Some 1 are very useful to man, for example, bees, 2 we get honey and wax, and silkworms, which 3 us with silk. Other varieties, 4 , are extremely harmful, and do a great 5 of damage, especially to crops. Locusts are perhaps the most dangerous of all, 6 they will eat almost any green 7 , and when millions of them 8 on cultivated land they soon leave it 9 . In some countries they are the farmers’ 10 enemy. Another nuisance is the common 11 , not only because it 12 us indoors and out-of-doors, but because it spreads diseases.

  Scientists have given much time and 13 to the study of insects. It needs the most careful and 14 observation. Thanks 15 their discoveries we now know almost all 16 is to be known about the habits of these hardworking insects, bees and ants, which live in 17 better planned in some ways than our 18 . But the most valuable work has been done in trying to give 19 to men, animals and crops from the 20 which insects cause.

1.A.members            B.forms        C.qualities           D.varieties

2.A.by which            B.from which     C.of which           D.in which

3.A.give                B.produce        C.offer              D.supply

4.A.however             B.meanwhile     C.offer             D.supply

5.A.majority             B.number        C.amount           D.what’s more

6.A.and                 B.for            C.if                D.when

7.A.grass               B.field          C.fruit              D.plant

8.A.settle               B.attack         C.pass              D.cross

9.A.bare               B.nothing        C.empty             D.untouched

10.A.hardest            B.greatest        C.serious            D.wildest

11.A.insect              B.creature       C.fly               D.enemy

12.A.dislikes            B.bites          C.worries           D.hates

13.A.understanding       B.ideas           C.comprehension      D.thought

14.A.serious            B.patient        C.curious           D.long

15.A.for                B.of            C.to                D.with

16.A.that               B.which        C.there             D.what

17.A.societies            B.crowds        C.teams             D.organizations

18.A.world              B.nation       C.selves             D.own

19.A.help              B.protection    C.living             D.defense

20.A.injury              B.wound       C.sickness            D.ruin

单项选择题