2. INTRODUCTION
• A file is an object on a computer that stores data, information, settings, or commands used with a
computer program.
• Commonly, files represent programs both source and object forms and data where data files may be
numeric, alphanumeric and binary.
3. FILE STRUCTURE
• Files must have structure that is understood by OS. Files can be structured in several ways. The most
common structures are:
1. Unstructured.
2. Record Structured.
3. Tree Structured.
4.
5. • Unstructured
Consist of unstructured sequence of bytes or words. OS does not know or care what is in the
file.Any meaning must be imposed by user level programs.
• Structured
Afile is a sequence of fixed-length records, each with some internal structure. Each read
operation returns one records, and write operation overwrites or append one record.
• Tree Structured
File consists of tree of records, not necessarily all the same length. Each containing a key field
in a fixed position in the record, sorted on the key to allow the rapid searching.
6. DIRECTORY
• Directory is a file system cataloging structure which contains references to other computer files,
and possibly other directories.
• Directories are known as folders, or drawersto provide some relevancy to a workbench.
7. TYPES OF DIRECTORY
• Single-level Directory
All files are contained in the same directory. Easy to support and understand; but difficult to
manage large amount of files and to manage different users.
• Two-level Directory
Separate directory for each user. Used on a multiuser computer and on a simple network
computers. It has problem when users want to cooperate on some task and to access one
another's files. It also cause problem when a single user has large number of files.
9. HIERARCHICAL DIRECTORY
• Generalization of two-level-structure to a tree of arbitrary height.
• This allow the user to create their own subdirectories and to organize their files accordingly.
• To allow to share the directory for different user acyclic-graph-structure is used.
10. PID (Process ID) and PPID (Parent Process ID) are system-generated unique
identifier numbers assigned to running processes in an operating system.
PID is a unique identifier for a process and is used to identify it for various
process-related operations such as signaling, killing, or inspecting its status.
PPID is the identifier of the parent process that created the process with the
given PID. This can be used to identify the hierarchy of processes and
determine which process launched another process.
Together, PID and PPID can be used to identify processes uniquely and provide
a clear picture of the process tree and the relationships between processes
