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Operating System Functions (Part 2)Operating System Functions (Part 2)3- Running Programs The operating system also provides the interface between the programs and the user. Through program, the user accesses other computer resources such as printer, backing storages or another application programs. Actually, in program the built-in instructions known as “system calls” are used that request the services from the operating system. For example, when you want to save a document in word processing program and Save command is applied, “Save As” dialog box appears. Similarly, when Open command is applied to open a document; “Open” dialog box is appeared with a list of files or documents. In this way, the program requests the services from the operating system. The application program sends the request to the operating system and the departing system gives the results back to the application program. Similarly, in data communication, information is sent and received via operating system. The main services that an operating system provides to programs are:
4- Managing Files The data and programs are stored permanently on the disk for future use. Application software such as word-processing, spreadsheet, database management system etc. may have hundreds oV files. The Windows operating system also has a large number of files. Similarly, when you prepare a document, in word processor, it is stored on the disk by giving a file name. The files are placed or stored in the folders or directories. A folder may contain files or sub-folders. The operating system keeps track of all the folders and files and sub-folders. The operating system maintains a list of these folders and files in the starting area of disk called the FAT (File Allocation Table). The FAT is created when the new disk is formatted by Operating system. The FAT area of disk contains the names of files, addresses of the disk where the data or contents of the respective files are stored. When new file is saved or name of file is changed or file is deleted, the operating system updates the information in the FAT. The operating system also keeps track of different disk drives by assigning names to them. For example, floppy disk drives are assigned letter A and B. The hard disk is assigned letters C and up. The CD-ROM drive has the first available letter following the hard drive(s) letters. The files are organized in folders so that you can quickly find or search the files, Folder can contain sub-folders. You can create a tree like structure known as hierarchical file system. You cast see the names of files and sub-folders in folder through the file viewer utility program. Windows Explorer is an example of file viewer utility program.
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