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Introduction of OS:

Definition: An Operating System is system software that controls the execution of application programs and acts as an interface between applications and the computer hardware.

 Fig 1: Operation System layout

Add in this picture Transistors, VLSI, and Organization with the level number. (NPTL)

Level 1: The lowest level consists of millions of transistors.

Level 2 (VLSI): At the next level these transistors composite together to build several logic gates like OR, AND, XOR, etc. along with memory cells. 

Level 3 (Organization): Now these basic VLSI units are then organized in various forms RAM, DECODE UNIT, etc. This organization is called hardware.

Now we are working with several different applications. Now operating system resides between the application and hardware layer. Application programs are executed with the intervention of hardware and this interaction is made by the operating system. Operating systems manage both applications which are executed on a computer and how resources are utilized in the system. 

Functions: 

• Time management.
• Resource allocator.
• Memory Management, Process, files, Security, etc.
• Scheduler.

Fig 2: A view of Operating System services

Goals:

  Convenience (Ease of Use i.e. User Friendly)

  Efficiency (System Resources to be used in an efficient manner)   

  Portability (Usability in different environments)   

  Reliability (Consistent performance)

  Scalability (Ability to evolve) 

Example:

The primary goal of Windows is Convenience. 

The primary goal of UNIX is Efficiency. 

Role of operating system to run application program:

The function of the operating system is to provide an environment in which a user can execute his/her commands or programs in a convenient and efficient manner. Lots of services are required to execute those application programs so that the user makes a request to get the services of an operating system by system calls i.e. system call is a function stub by which the services of the user programs are requested to operating systems. Now the main module of operating systems is the kernel and some non-kernel routines which are mainly responsible to provide and support the services of the operating system to run the t user’s application program. System calls are the only entry points into the kernel system. So, all users’ programs demanding resources for execution must use system calls. 

Another important part of OS is the command interpreter; the main role of the command interpreter to make an interface between the program and the kernel. When a user tries to execute a program, the command interpreter of the user interface makes a system call with the name of the program as a parameter. At the lowest level, system calls allow a running program to make requests from the operating system directly. At a higher level, the command interpreter or shell provides a mechanism for a user to issue a request without writing a program.

The software that contains the core components of the operating system is called Controller.

Fig 3: An overview of Operating System