Extended services - These are add-on modular software components that are layered on top of base service.
Common types of Services 1.Execution of Program
This is the first and foremost services that is provided by the operating system to users. The computing system must execute and terminate all user programs successfully by loading them into main memory. A proper error message must be displayed for the incomplete programs. 2.Input/output operations
During normal execution of a program user may be required to input data or may need some processed data as output. It is the job of the operating system to obtain data from the input device or from some data files and send the output to a data file or output device. 3.File Management
The user of the computing system may need to create the files on secondary storage to record their work permanently for future use or delete the file that is already in existence. The operating system must provide a mechanism that carefully handles all these file manipulation operations on the respective devices. 4.Communication
In the computing system there can be more number of programs that need to share information among them. The program may be running on a single machine or may be run on several machines. This phenomenon is known as ?Inter process communication?. To maintain data security and integrity, an operating system must handle inter process communication. 5.Error detection
If any recourses or device in a computing system comes across any error it should be promptly handled by the operating system. Invalid or improper use of devices by the programs must be reported. The most common types of errors are: memory allocation error, divide by zero error, power off error etc. 6.Protection
The operating system should provide the services to all users by ensuring the security of access by authenticated users to same important files and data. 7. Accounting
In case of multiple users of the computing system the information of duration and number of resources that are used by each user may be tracked by the operating system for accounting purpose. 8.Resource Sharing and Allocation
When there are more number of users in the computing system or there are many programs competing for limited resources, then the optimal allocation and de-allocation of resources are the responsibility of operating system to ensure increased throughput.