By structuring the pointers in a geometric fashion, a single i-node can represent a very large file. The operating system traces its way through a file path by following the i-nodes until it reaches the direct pointers that contain the actual location of the file on the storage device. Each file system that is mounted on a UNIX machine is accessed through its own block special file. It includes information about the name of the device, the directory name under which it will be mounted, and the read and write privileges for the device. Although not originally part of the UNIX filesystem, quotas quickly became a widely-used tool.
Quotas allow the system administrator to place limits on the amount of space the users can allocate.
Quotas usually place restrictions on the amount of space, and the number of files, that a user can take. The limit can be a soft limit , where only a warning is generated, or a hard limit , where no further operations that create files will be allowed. The command quota will let you know if you're over your soft limit. Adding the -v option will provide statistics about your disk usage. If you get an account on an unfamiliar UNIX system, take a tour of the directories listed above, and familiarize yourself with their contents.