FILE SYSTEM

1.What are the most common schemes for defining the logical structure of a directory?

The most common schemes for defining the logical structure of a directory

•  Single-Level Directory

•  Two-level Directory

•  Tree-Structured Directories

•  Acyclic-Graph Directories

•  General Graph Directory

2.Define UFD and MFD.

In the two-level directory structure, each user has her own user file directory (UFD). Each UFD has a similar structure, but lists only the files of a single user. When a job starts the system's master file directory (MFD) is searched. The MFD is indexed by the user name or account number, and each entry points to the UFD for that user.

3.What is a path name?

A pathname is the path from the root through all subdirectories to a specified file. In a two-level directory structure a user name and a file name define a path name.

4.What are the various layers of a file system?

The file system is composed of many different levels. Each level in the design uses the feature of the lower levels to create new features for use by higher levels.

•  Application programs

•  Logical file system

•  File-organization module

•  Basic file system

•  I/O control

•  Devices

FILE SYSTEM

A file in UNIX is nothing but a storehouse of information and everything is treated as a file by UNIX. The files can be broadly classified as follows:

􀂾 Ordinary files—Contains stream of data. All data, text, source programs, object and executable code, commands fall into this category.

􀂾 Directory files—Contains no external data. It contains an entry, name of the file and its inode (identification number) for each file and subdirectory under that directory.

Directory files are not created by the user but by the UNIX system itself.

􀂾 Device files—Even physical devices are treated as files. These are special in the sense that any output directed to it will be reflected onto the respective device.

All files in UNIX are related to one another. The file system of UNIX resembles a tree that grows from top to bottom as shown in the figure. The file system begins with a directory called root (at the top). The root directory is denoted by a slash (\). Branching from root there are several directories such as bin, lib, etc, tmp, dev. Each of these directories contains several sub-directories and files.