Operating System
OS is an important system software package found in every computer system. It is a set of programs that controls and supervises a computer system’s hardware and it provides services to computer users. It permits the computer to supervise its own operations by automatically calling in application programs and managing data needed to produce the output desired by users. OS is an interface between the user and the computer. OS perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers. OS, as a resource manager keeps track of who is using which resource, to grant resource requests, to account for usage and to mediate conflicting requests from different programs and users.
Functions of an Operating System:
Job Management: OS manages the jobs waiting to be processed. It recognizes the jobs, identifies their priorities, determines whether the appropriate main memory and secondary storage capability they require is available, and schedules and finally runs each job at the appropriate moment.
Batch Processing: Data are accumulated and processed in groups. The printing tasks in the printer are also done in groups. Most of the tasks of OS are grouped and performed one by one. On-line Processing: In on-line processing, data are processed instantaneously. Most on-line operating systems have multi-user and multitasking capabilities. Now a day we can access the data from the remote sites using on-line processing.
Data Management: OS manages the storage and retrieval of data. As the system software handles many of the details associated with this process, such details are not a primary concern for users or programmers writing application programs.
Virtual Storage: Using this method the capacity of main memory increases without actually increasing its size. This is done by breaking a job into sequences of instructions, called pages or segments, and keeping only a few of these in main memory at a time; the remaining are kept on secondary storage devices. Thus, relatively large jobs can be processed by a CPU.
Input/ Output Management: OS manages the input to and output from a computer system. This applies to the flow of data among computers, terminals, and other devices such as printers. Application programs used the operating system extensively to handle input and output devices as needed.
Function of operating system can be further listed as follows:
- User interface implementation
- Share hardware implementation
- Allows users to share data.
- Prevent users from interfering with one another.
- Scheduling resources among users.
- Facilitate input/output
- Facilitate parallel operations
- Organize data for secure and rapid access.
- Handle network communications
Classification of Operating System:
Multi-user: These systems allow two or more users to run programs at the same time. Some OS permit hundreds or even thousands of concurrent users. The operating systems of mainframes and minicomputer are multi-user systems. Examples are MVS, UNIX, etc. Another term for multi-user is time-sharing.
Multiprocessing: It refers to a computer system’s ability to support more than one process (program) at the same time. This system allows the simultaneous execution of programs on a computer that has several CPUs. Mainframe, Supercomputers have more than one CPU.
Multitasking: This system allows a single CPU to execute what appears to be more than one program at the same time when, in fact, only one program is being executed. In multitasking, only one CPU is involved, but it switches from one program to another so quickly that it gives the appearance of executing all of the programs at the same time.
Multithreading: Multithreading allows different parts of a single program to mn concurrently. Multithreading is the ability of an OS to execute different parts of a program, called threads, simultaneously.
Real-time: These operating systems are system that responds to input immediately. It allows a computer to control or monitor tasks perfonned by other machines and people by responding to the input data in the required amount of time.
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