In root directory of logical driver, we may directly create files as well as primary directory, that is called the sub-directory under the root directory. Correspondingly, the root directory is called parental directory of the sub-directory. The sub-directory and the parental directory are relative, a parental directory may have many sub-directories, while a sub-directory has only one parental directory. In sub-directory, we can also create more sub-directories of lower level, thus forming the directory tree. For sub-directory, its entrance is still in root directory. The content of root directory FDT in sectors is:
The first directory registration entry is volume label whose attribute byte (0BH byte) is 08H. The 2nd is the registration entries of the sub-directory "123". The 3rd is the registration entries of the file "file1.txt".
Establish a "C" sub-directory under its root directory. The analysis chart of "C" file directory is:
According to the root directory folder chart, compared to the files in root directory, the expressive way of directory name and filename is the same; and so is that of start cluster except that of attribute and length. For folder, the fixed length is "0". Setting like this is for the convenience of system administration, otherwise, any change to the folder will affect the efficiency of management; moreover the size of directories can not define properly, it might conflict with the file length. As the same, like the root directory structure, the content storage in folder saves separate file directory entry whose management is similar to that in root directory. But there are still some differences between sub-directory and the root directory, which lie in their own management of their own management: the root directory is determined by DBR, while sub-directory is determined by the directory registration entry under root directory. That is because these sub-directories are created by root directory. For sub-directory, it is necessary to discuss the first two sub directories as following:
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