What is Unix?
- Unix is a layered OS which is an abstraction between the user and the hardware.
- Unix is multiuser and multitasking OS. Unix supports multiple parallel users working on multiple software application tasks.
- The core of Unix is the Kernel which takes commands with the help of Shell.
The UNIX operating system is made up of three layers between the user/applications and the hardware.
- The Kernel – The kernel is the core of Unix OS. It interacts with hardware. It performs the critical part of the OS like task scheduling, memory management, and filesystem management. Here are some subsystems owned by the kernel.
- Virtual Memory Management
- Virtual Filesystem
- System Calls – System calls are the only interfaces which are used to request services from the kernel. These limited number of entry points are well documented in Unix programmer’s manual.
- The Shell and the libraries – Shell is command line interpreter which takes a sequence of commands as input and invokes appropriate system calls. Libraries are ready-made utilities for day to day activities like copy files (cp), created a directory (mkdir), etc.