UNIX Architecture

There are two major agencies on which UNIX depends are :Kernel and Shell. The Kernel interacts with the machines hardware, and the Shell is interacts with the user of the machine. The diagram below shows the architecture of UNIX

Kernel

• It is the core of the operating system, a collection of routines mostly written in C.
• It is loaded into memory when the system is booted and communicates directly with the hardware.
• User programs/applications that need to access the hardware like hard disk or terminal that use the services of the kernel, which performs the job on the users behalf. These programs access the kernel through a set of functions called system calls.
• It manages the systems memory, schedules processes, decides their priorities, and performs other tasks.

Shell

• Computers don't have any inherent capability of translating commands into action. That requires a command interpreter, a job that is handled by the "Outer Part" of the operating system.
• Shell is interface between the user and kernel. Even though there's only one kernel running on the system, there could be several shells in action-one for each user who is logged in.