How Unix works ?

Unix is a layered operating system.

The innermost layer is the hardware that provides the services for the OS.

The operating system, referred to in Unix as the kernel, interacts directly with the hardware and provides the services to the user programs. These user programs don’t need to know anything about the hardware.

The shell acts as an interface between the user and the kernel.

User programs interact with the kernel through a set of standard system calls. These system calls request services to be provided by the kernel. Such services would include accessing a file: open close, read, write, link, or execute a file; starting or updating accounting records; changing ownership of a file or directory; changing to a new directory; creating, suspending, or killing a process; enabling

access to hardware devices; and setting limits on system resources.

Unix is a multi-user, multi-tasking operating system. You can have many users logged into a system  simultaneously, each running many programs. It’s the kernel’s job to keep each process and user separate and to regulate access to system hardware, including cpu, memory, disk and other I/O devices.