An operating system(OS) is an intricately woven fabric of programs.The programs are usually coded in the assembly language and are specific to the processor around which the computer is built. The unix OS ,on the contrary, is written largely in the 'C' language which is not processor dependent. However, part of the unix os is written on the Assembler. This makes Unix highly portable- which means that it can run on various processors with little modification.
The structure of the Unix OS makes it a better OS as compared to other conventional operating systems.
The responsibilities of an OS include command interpretation,I/O control, communications and a lot more .To perform these tasks a large number of simple as well as complicated programs are needed. These programs can be independent or interdependent. In conventional operating systems, all these programs are put together forming one large program that occupies a large amount of memory. Therefore the system response is very slow. Unix with a fresh structural approach does not slow down the system.
The Unix system can be divided into four major units. These units work together but are still separate so that one large portion of the memory does not get blocked and slow the system down.
The four units are:-
1. Kernel- A core unit that interacts with the hardware for low-level functions. The kernel is a program that constitutes the nucleus of the operating system. It co-ordinates the internal functions of the computer, such as allocating system resources. The kernel works invisibly. The user will never be aware of it while working on the system.
2.Shell- An outer unit that interacts with the user to perform functions desired by the user. The shell is a program that acts as a liason between the user and the kernel by interpreting and executing user commands. As it reads user input and sends messages to the user it is described as interactive.
3.Commands - Commands are compiled C programs that perform a specific operating system job. These commands are invoked by name through the shell. Unix has very few in- built commands(internal commands) like 'echo'and 'pwd'. For these no separate C compiled programs are required. These are the shell's inbuilt features and the shell is able to interpret them itself. Unix commands perform a range of functions like editing, copying , erasing files, sending and receiving emails etc.
4.File System- The file system is a collection of all the files available on the computer. It allows you to store and retrieve information easily.