What is UNIX ?

UNIX is a operating system which is multi user (multiple user can access Unix system at a same
 time ) and  multitasking (One user can run multiple program). Operating System is an interface
 between hardware and applications software's.

Unix Architecture

1.Shell

• Human interface point for Unix
• Program layer – provides an environment for the user to enter commands to get desired results.
• Korn Shell, Bourne Shell, C Shell are various shells used by Unix users

2. Kernel

• Heart of The Unix OS.
• Collection of C programs directly communicating with hardware
• Part of Unix system loaded into memory when Unix is booted

        Manages:-

• System resources
• Allocates time between user and processes
• Decides process priorities

3.  Hardware

 Unix Boot Process Setps

1. BIOS    : Basic I/O System Executes MBR.
2. MBR : Master Boot Record Executes GRUB.
3. GRUB  : Grand Unified Boot loader executes Kernel.
4. Kernel : Kernal executes  sbin/Init.
5. Init          : Init executes run level programs .
6. Runlevel : Runlevel program executes from /etc/rc .d/rc*.d/rc*.