设计目录结构（采用多级目录）以及文件目录项的结构、外存空间的位示图，并编程实现如下要求（本实验未考虑实现文件操作功能）-Design the directory structure (using multi-level directory), and the file directory of the structure of space-bit Out-of-Core that map, and programming to achieve the following requirements (in this experiment does not take into account file operation function)