《Operating System Concepts》学习第 44 天，p495-p511 总结，总计 17 页。
一、技术总结
1.cache
(1)定义
A cache is a region of fast memory that holds copies of data.
(2)cache 和 buffer 的区别
The difference between a buffer and a cache is that a buffer may hold the only existing copy of a data item, whereas a cache, by definition, holds a copy on faster storage of an item that resides elsewhere.
2.spool
(1)定义
A buffer that holds output for a device (such as a printer) that cannot accept interleaved data streams.
二、英语总结(生词：2)
1.urgency
(1)urge: urgere(“press hard, push forward”)
vt. try strongly to persuade sb to do sth.
(2)urgent
adj. very important and needing attention immediately(紧急的)。
(3)urgency: urgent + -cy
u. the quality of being very important and needing attention immediately(紧急性，紧迫性)。
(4)示例
We need multilevel interrupts, so that the operating system can distinguish between high- and low-priority interrupts and can respond with the appropriate degree of urgency when there are multiple concurrent interrupts(《Operating System Concepts》第 495 页)。
2.reserve
(1)reserve: re-(“back”) + servare(“to keep”)
vt. to keep back for further use。
(2)示例
Most CPUs have two interrupt request lines. One is the nonmaskable interrupt, which is reserved for events such as unrecoverable memory errors(《Operating System Concepts》第 496 页)。
(3)reserve vs preserve
reserve: to save sth for later use。
preserve: maintain sth in its original manner/state。
关于英语的注解同步更新汇总到 https://github.com/codists/English-In-CS-Books 仓库。
三、其它
今天没有什么想说的。
四、参考资料
1. 编程
(1) Abraham Silberschatz，Peter Baer Galvin，Greg Gagne《Operating System Concepts》：https://book.douban.com/subject/30272539/
2. 英语
(1) Etymology Dictionary：https://www.etymonline.com
(2) Cambridge Dictionary：https://dictionary.cambridge.org
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