Used to synchronize access to the file control block 用于同步对文件控制块的访问。
File control block fc 档案控制区块
百科解释
A File Control Block (FCB) is a file system structure in which the state of an open file is maintained. An FCB is managed by the operating sytem, but it resides in the memory of the program that uses the file, not in operating system memory.