As we have already seen how a computer uses all its components and peripherals to carry on computing and various other operations. These devices which are used are hardware devices, which usually require instructions to work as they cannot work by themselves. The memory has to be managed, input/output operations have to be done and various other functions have to be done, which are accomplished by giving necessary instructions, which are given in machine understandable form.
Each machine is different from other machines in configuration. Therefore, it becomes quite difficult and nearly impossible task for the programmers to write instructions for the above operations. It still programmers manage to do this, they will be wasting their precious time and effort by concentrating more on making the computer work rather than getting their tasks done. Therefore emerged the search for a common tasks thereby leaving only the task programming for specific tasks, which resultant in the development of operating system, a system software, which will do all the above tasks as well give an environment to work with computer.
The operating systems act as an extended machine as it acts in the similar way as hardware, which helps the user to program his task. The operating systems de-link user from hardware, they help the programmer to get his tasks done by acting as mediator between the user and the hardware.
Meaning of Operating System in Full Form
Operating Systems: Operating systems (OS) can be defined as “Set of programs that are capable to manage resources as well as the operations of a computer”. Operating systems hide the hardware Virtually from the user it isolated the hardware from the user till the functions are performed property user is not concerned about the hardware specification the above figure out how the operating system isolated hardware from the user operating systems have been on the evolutionary through the years this evolution was for the development of more and more better operating systems with better features the basic function which are carried by any operating systems are:
Assigning processor for performing test allocating memory managing memory and other storage areas command interpretation handling job to job transition, maintaining internal clock scheduling of various job task establishing and enforcing period for defect jobs coordinating and managing peripheral devices
input output management establishing datasecurity and integrity
Operating systems concept with Full Education
User programs interact with operating systems using set of extended instructions. The interactions are called “System Calls”. These system calls are used to create, delete and use various software objects that are managed by the operating systems. The most commonly used and important system calls or processes and files. The following features are common in any operating system:
Processes: Process is one of the most vital concepts of an operating system. We can define operations as a program in execution. Process is composed of an executable program; the data used by the program and just take the program and the stack, the program counter, registers, stack pointer and any other information which is required for the execution of the program. To understand concept of process easily, let us discuss about the time sharing operating systems where the CPU time is shared by many processes, where a process after being given its share of time was suspended and an another process get the timeshare.
Once its time share is completed it comes back to the suspended process, which as a matter of common sense, should start from, the position where it was suspended and this operation cycle goes on. To keep track on ongoing process is most of the operating systems maintain a perfect table, which usually each and every where the information is stored.
The basic system calls or process management are those which deals with the creation and termination of process. For example, consider a process like cell or common interpreter, which reads the given commands from a Terminal, Once a user give a command, shell has to create a new process which is going to execute the given command and once the execution is complete, the process has to terminate. There are many other processes like memory management, child process management, message management etc which makes an Operating System efficient and workable.
Files: There another broad category of system calls which are used to work with file system. As we have already seen that once of the basic functions of an operating system is to hide the hardware from the user, so that he is not bothered about any interaction with hardware as the interactions are taken care while operating system, therefore when a user works with the file system, calls are needed for the creation of files, maintenance of files reading from the files writing to files etc., as well as opening of file Before any operation and closing the file after the users are all taken care of by the system calls.
The concept of directory that each folder of files, where a user can group his files together, has to be provided for which system calls is required. In a directory, a user can have either files or other directory. This concept of directory is provided so that and user can grow up his files all directories which are similar in one or the other aspects, which makes his search as well as access easier. Both the process and files follow the hierarchies, which are organized as trees. This is where processes and files are similar to each other. Usually process hierarchies are not very deep, there is usually at most three levels of hierarchies where as the files can have hierarchies which are very deep and they can go up to five, six or more level deep.
The lives of personalities are very short and general and most few minutes where the file is exists last longer with many years as lifespan.
System calls: For every task to be done, user has to interact and communicate with the computer by operating system. All the users programs communicate with the operating system for various services and caused by making systems calls
. Every system call has a library procedure that user programs can call. These procedures of the parameters of the systems call at specified areas, such as registered etc and issue of TRAP instruction, which is protected procedure call, to start the operating system. The basic purpose library procedure is to hide the TRAP instruction details so that the systems calls look like ordinary procedure calls
After the receipt of the procedure call the operating system checks the parameters for validity and if valid, performs the work requested. After the requested task is finished, the operating system update the state code in the register, starting whether the given task is executed successfully or it failed and then execute an instruction to return from the TRAP to the library procedure. Later this library procedure returns the user the function value and other values as parameters.
The shell: We have already seen that it is the code of operating system which carries the system calls. Along with operating system other system software like editors, compilers, assemblers, linkers, command interpreters etc also come as helping hand and are quite important. The shell is command interpreter of the UNIX operating system. We look into the concept when we are discussing UNIX operating system is following chapters.
At present let us understand the shell, even though is not the part of operating system, uses many operating system features and is one of the best examples of how system calls can be used. Shell is also the primary interface between the user and the operating system, which starts as soon as user logs on the system.
Operating system is collection of program which is used to control the operating computer system
i.e. the Peripheral device and other utilities. The operating system is partly stored in the secondary memory storage device like hard disk, magnetic tape etc and partly store permanently in the ROM i.e. Read Only Memory.