2. 计算机
  3. The following scenario applies to questions 30, 31, and 32. Operating systems have evolved and changed over the years. The earli

The following scenario applies to questions 30, 31, and 32. Operating systems have evolved and changed over the years. The earli

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问题 The following scenario applies to questions 30, 31, and 32.
Operating systems have evolved and changed over the years. The earlier operating systems were monolithic and did not segregate critical processes from noncritical processes. As time went on operating system vendors started to reduce the amount of programming code that ran in kernel mode. Only the absolutely necessary code ran in kernel mode, and the remaining operating system code ran in user mode. This architecture introduced performance issues, which required the operating system vendors to reduce the critical operating system functionality to microkernels and allow the remaining operating system functionality to run in client/server models within kernel mode.
Which of the following best describes the second operating system architecture described in the scenario?
选项 A、Layered
B、Microkernel
C、Monolithic
D、Kernel based
答案B
解析 B正确。在微内核体系结构中，只有数量减少的代码在内核模式中运行，执行关键的操作系统功能。只有完全需要的代码才在内核模式中运行，其他的操作系统代码都运行在用户模式。传统的操作系统功能，比如设备驱动、协议栈和文件系统，都已经从微内核模式中移出，换到用户空间中执行。
A不正确。因为分层的操作系统体系结构侧重于将操作系统的功能进行分层。这种体系结构并不关注什么在内核模式执行，什么不在内核模式执行。
C不正确。因为这个行业起始于单片集成的操作系统，并由此演变。单片集成的操作系统并不隔离特权进程与非特权进程，也不使用内核。MS-DOS就是单片集成的操作系统的例子。
D不正确。因为尽管不存在叫做“基于内核的”官方体系结构，但这个答案实际上并没有正确地解决减少运行于内核模式的代码的概念。微内核体系结构则明确地解决了这个问题。微内核是实现操作系统所需机制的几乎最少量的软件。
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