User perspectives provided in the Unix:

The file system

The characteristic of UNIX file systems are

• A hierarchical structure
• Consistent treatment of data
• Ability to create and delete files
• Dynamic growth of files
• Peripheral devices also treated as files

The file system is organized in the form of a tree. The root node is called "root" and is denoted as "/". Every non-leaf node in this structure is directory and every leaf node is a file or a special device. The file is identified by its full path like /var/www/index.html

Processing environment

The source code (programs) is written by users in some programming language. This source code is executed and an executable file is generated. Finally, this executable file is run. This instance of our program in execution is called process. Many processes can execute simultaneously in UNIX. Also, many instances of one program can run simultaneously. The state of processes can be controlled by various system calls.

Building block primitives

Unix allows the user to write small programs, in a modular way. These programs can be used as building blocks for complex programs. A Unix system call is a direct request to the kernel if a system resource is needed. It might be a request for a file descriptor to manipulate a file or to write to a file, or any of the hundreds of possible operations. These are exactly the building blocks on which every Unix program is built upon.

UNIX has 3 standard files.

1. Standard Input file
2. Standard output file
3. standard error file