Operating system (concept)

The generalized structure of the software

OS performs control functions by computation processes, distributes resources between different computation processes and forms software environment in which application programs of users are executed.

"Any of components applied program providing works running OS and has no direct access to the computer equipment. Even users interact with the programs via the OS interface. Any commands before being included in the application program, at first pass through OS."

There are two groups of determinations of OS: "set of the programs managing the equipment" and "set of the programs managing other programs". Both of them make the exact technical sense which, however, becomes clear only by more detailed consideration of a question of that why in general operating systems are necessary;

There are applications of ADP equipment for which OS are excessive. E.g., the built-in microcomputers contain today in many household appliances, cars (sometimes ten in everyone), cell phones, etc. Often such computer constantly performs only one program which is started after inclusion. And simple game consoles — also representing specialized microcomputers — can do without OS, starting at inclusion the program written on the "cartridge" inserted into the device or a compact disk. (Many built-in computers and even some game consoles actually work running the OS).

Operating systems, in turn, are necessary if:

• the computing system is used for different tasks, and the programs performing these tasks need preserving of data and exchange of them. From this need of the universal mechanism of preserving of data follows; in most cases OS responds to it with implementation of the file system. Modern OS, besides, give an opportunity directly "connect" an output of one program with input another, passing rather slow disk transactions;
• different programs need accomplishment of the same routine actions. E.g., simple input of the character about keyboards and display it on the screen can demand execution of hundreds of machine instructions, and disk transaction — thousands. Not to program their every time again, OS provide system libraries of often used subprogrammes (functions);
• between programs and users of a system it is necessary to distribute powers that users could protect the data from others look, and the possible program error did not cause total troubles;
• the possibility of the simulation of "simultaneous" execution of several programs on one computer (even containing only one processor) performed using the acceptance known as "time sharing" is necessary. At the same time the special component called by the scheduler "cuts" CPU time on short segments and provides them in turn to the different performed programs (processes);
• at last, the operator should have an opportunity, anyway, to manage processes of accomplishment of separate programs. For this purpose operating environments, one of which — a cover and a set of standard utilities — is a part of OS, serve (other, such as graphical operating environment, form applied platforms, independent of OS).

Thus, modern universal OS can be characterized first of all as

1. the using file systems (with a universal data access mechanism),
2. multi-user (with separation of powers),
3. multitask (with time sharing).