问题 单项选择题

响应比高者优先的作业调度算法是以计算时间和 (26) 来考虑的。

A.中断时间

B.完成时间

C.运行时间

D.等待时间

答案

参考答案:D

解析:[分析]
响应比高者优先调度算法是在每次调度作业运行时,先计算后备作业队列中每个作业的响应比,然后挑选响应比最高者投入运行。响应比定义如下:
响应比二作业响应时间/运行时间的估计值
其中,响应时间为作业进入系统后的等待时间加上估计的运行时间。那么又可以得出:
响应比=1+作业等待时间/运行时间的估计值
因此,可以推导出响应比高者优先的作业调度算法是以计算(运行)时间和等待时间来考虑的。

选择题
阅读理解

Cast your mind back to the past twenty years and hardly did anyone have their own email account. The Internet had just taken off in 1991 and people were only using office and PC­based email exchanges.

In the mid 1990s external email providers appeared. The most famous of these was Hotmail, the first free email provider and web­based email service. Sabeer Bhatia and Jack Smith launched Hotmail on July 4, 1996. And Microsoft took note of and bought Hotmail for $400 million on December 30, 1997, a nice birthday present for Bhatia who turned 29 that day. It was relaunched as MSN Hotmail and in 2007 was relaunched again as Windows Live Hotmail.

Fast forward the present day and most of us have at least a personal web­based email account. It seems impossible to live without them. One of the biggest advantages of email is the fact that communication has become so much easier, especially with those across different time zones. Email takes seconds to send a message whereas letters, as we used to communicate by, could take weeks. Of course there was the fax, that beeping invention from the 1980s, but it wasn’t as secure as email and you never knew if the person on the other end had picked up your fax or if it had got lost somewhere in the office.

In conclusion, one of the best inventions from the 1990s has to be email. But sometimes people are too closely connected to their email and have a compulsion to check it several times a day. At work, people have become lazy and instead of going to speak to the person sitting next to them, they send an email,causing an in box to pile up with more time spent reading email and responding rather than working. Clearly, an invention that saved time because of its quick and speedy connection can now also cause us to waste a lot of time.

小题1:The earliest web-based email came into being probably _______.

A.in 1991

B.in 1996

C.in 1997

D.in 2007小题2:The author mentions “fax” in the third paragraph in order to tell us that _______.

A.it is exactly as good as email

B.it is much better than email

C.it is less convenient than email

D.it is easier and faster than email小题3:The underlined word “compulsion” in Paragraph 4 probably means “_______”.

A.strong desire

B.common sense

C.special curiosity

D.general idea小题4:Which is the main idea of the last paragraph?

A.We should check email boxes frequently.

B.Lazy people like sending an email.

C.Email brings us great convenience.

D.Good inventions also cause problems.