在内存中开辟一个空间作为文件存储器，在其上实现一个简单的文件系统。退出这个文件系统时，需要该文件系统的内容保存到磁盘上，以便下次可以将其回复到内存中来。-In memory to open a space for the file memory, in its realization of a simple file system. To withdraw from the file system, the need for the contents of the file system is