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【单选题】

(11)处应填()。

A.243ms
B.246ms
C.254ms
D.280ms

A.
假设磁盘上海个磁道划分成9个物理块,每块存放1个逻辑记录。逻辑记录R1,R2,…, R9存放在同一个磁道上,记录的安排顺序如下表所示。
B.
C.
假定磁盘的旋转速度为27ms/周,磁头当前处在R1的开始处,系统使用单缓冲区,当缓冲区内容处理完时才能再存放新的记录,且每个记录的处理时间为3ms。若系统顺序处理这些记录,则处理这9个记录的最长时间为 (11) ;若对信息存储进行优化分布后,处理这9个记录的最少时间为 (12)
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【单选题】安全电子邮件协议PGP不支持()。

A.
确认发送者的身份
B.
确认电子邮件未被修改
C.
防止非授权者阅读电子邮件
D.
压缩电子邮件大小

【单选题】(75)处应填()。 A.application B.session C.physical D.transport

A.
TCP/IP (71) layer protocols provide services to the application (72) running on a computer. The application layer does not define the application itself, but rather it defines (73) that applications need — like the ability to transfer a file in the case of HTTP. In short, the application layer provides an (74) between software running on a computer and the network itself. The TCP/IP application layer includes a relatively large number of protocols, with HTTP being only one of those. The TCP/IP (75) layer consists of two main protocol options — the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP).