《Operating System Concepts》阅读笔记：p203-p207

《Operating System Concepts》学习第 23 天，p203-p207  总结，总计 5 页。

一、技术总结

1.vmstat

Linux 系统上 vmstat 命令的作用是“Report virtual memory statistics”。

2.scheduling algorithms

(1)FCFS(first-come first-serve)

(2)SJF(shortest-job-first)

准确的叫法应该是“shortest-next-CPU-burst”。

二、英语总结(生词：4)

1.convoy

(1)convoy: con-("together") + via("road")

c. a group of vehicles traveling together(车队，船队等)。

vt. accompany (a group of vehicles) for protection(护送)。

(2)示例

There is a convoy effect as all the other processes wait for the one big process to get off the CPU(《Operating System Concepts》第 207 页)。

以下是个人的理解：其它所有进程(all the other processes)排在一个重量级的进程(one big process后等待，这种场景很像“护送，护航”，所以称为“convoy effect”，effect的意思是"a result or consequence of an action "。convoy effect 直译就是“护航效应”、“护送效应”。

2.disastrous

(1)disaster: dis-("ill") + astro("star, planet")

c/u. great harm。

(2)disastrous: adjective form of disaster。

adj. extremely bad。

示例：It would be disastrous to allow one process to keep the CPU for an extended period(《Operating System Concepts》第 207 页)。

3.provable

(1)prove: *per-("forward") + *buh("to be")

vt. to show sth is true。

(2)provable:

adj. be able to be proven。

(3)probably:

adv. in a way that be able to be proven。

示例：The SJF scheduling algorithm is provably optimal, in that it gives the minimum average waiting time for a given set of processes(《Operating System Concepts》第 207 页)。

4.optimal & optimum

(1)optimal: optimum + -al

adj. best。

(2)optimal vs optimum

optimum也可以做形容词，意思和 optimal 一样，意为"best"。看到一种说法是“In some areas of mathematics, an optimal value is essentially a local optimum; i.e. it's an optimum value in its neighborhood.”。这里记录一些用例，方便后续比较，理解。

The SJF scheduling algorithm is provably optimal, in that it gives the minimum average waiting time for a given set of processes(《Operating System Concepts》第 207 页)。

三、其它

今天没有什么想说的。

四、参考资料

1. 编程

2. 英语