- It is the interface between hardware and user.
- It is responsible for management and coordination of activities and sharing of resources of computer.
- It acts as host for computing applications that run on the machine.
- The applications access OS services through APIs or System Calls.
- It provides two types of interfaces to the users, namely Command Line Interface and Graphical User Interface.
History of Unix and Linux
- In 1969, UNIX first originated in form of Multics at Bell Laboratories.
- In 1974, Thompson and Ritchie both published a paper regarding UNIX in Communications of ACM.
- By 1977, several UNIX systems were used in Universities.
- During 1977 to 1982, UNIX System III was released by Bell Laboratories.
- By the start of 1984, the use of UNIX systems significantly increased.
- Linux is a complete rewrite of Unix, developed by Linus Tourvalds, when he was a Finnish undergraduate.
Features of Unix
Unix OS can be installed on any architecture.
Multiple users can access the system and share its resources.
Multiple tasks can be initiated and run simultaneously.
Server shares CPU time between requesting processes.
- Hierarchical file organization
The / (root) is at the top of hierarchy and the various other file systems are below that.
Architecture of Unix
- Unix utilities
Architecture of Unix: System components
Architecture of Unix: Kernel
- This is the core of Operating System.
- It functions as the Hardware interface.
- It contains system calls that perform low-level tasks.
- It generates inode numbers for newly created files and maintains inode tables.
- It generates process identifications (IDs) for newly created processes and maintains process control blocks.
Architecture of Unix: Shell
- User interface
Shell provides an interface to the user, wherein the user could issue his commands, and Shell displays output and error messages to the user.
- Command interpreter
Shell accepts command from user, and interprets it to the kernel.
- Command processor
Shell parses the command line arguments, expands the special meaning of meta characters, searches for the command, and if the command is found, then transfers control to the command.
- Programming language
Shell provides a native programming language.