Computers store data in a series of directories. Each directory, or folder, may contain files or other directories. If a directory is located within another directory, it is called a subdirectory (or subfolder) of that folder. Subdirectories may refer to folders located directly within a folder, as well as folders that are stored in other folders within a folder. For example, the main directory of a file system is the root directory. Therefore, all other folders are subdirectories of the root folder.
The contents of your computer's operating system are organized using subdirectories. After all, you can imagine how hard it would be to locate documents on your computer if they were all stored in a single folder. By using subdirectories, users can navigate through folders in a logical hierarchy.
For example, in Windows, the C: drive contains a "Documents and Settings" subdirectory. Within this directory, are subdirectories for each user of the computer. Within each user's folder are other subdirectories, including "Desktop," "My Documents," and "Start Menu." In Mac OS X, the main hard disk contains a "Users" folder. This directory contains a list of all the users' home folders. Within each user's home folder are several other subdirectories, such as "Documents," "Movies," and "Music."
Both Windows and Mac users can create subdirectories to further organize data within these predefined folders. This can be useful when categorizing data on your hard drive. For example, if you store all your digital photos within the "Pictures" folder, you might create subdirectories that are named by date, such as "2009-06-01," "2009-07-04," "2009-08-15," etc. You could also create subdirectories based on the source of each image, such as "Digital Photos," "Screenshots," and "Scanned Images." Regardless of what folder names you choose, creating subdirectories can save you a lot of time when browsing through files in the future.