buffer和cache

A buffer is something that has yet to be(有待) "written" to disk. A cache is something that has been "read" from the disk andstored for later use. Buffer的核心作用是用来缓冲，缓和冲击。比如你每秒要写100次硬盘，对系统冲击很大，浪费了大量时间在忙着处

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