buffer is one piece of memory section, it is usually 4Kb in Linux. It is mainly used between different devices with different speed or different priorities. With buffer, the waiting time between different processes will be reduced. Here is one simple example, when you type something in a text editor, every time when you type a character, the operating system will not write it to the disk directly, instead it will write it to buffer first When the buffer is full, the data in the buffer will be written to disk. But when you call flush(), the data in the buffer will be written to the disk immedia...