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Application libraries in the system

As time passed, operating system designers began to add more and more abstractions to handle file management, printing, graphics, and other programming tasks. Programmers in turn began to create more complex applications that took advantage of these capabilities and added new ones. In the 1980s, as shown in the middle of Figure 1, system software such as Mac OS, Windows, and OS/2© expanded to include application libraries that developers could use to add new capabilities to their applications, including menus, windows, dialog boxes, networking, telecommunications, interapplication communication, and so on.

For example, a Mac OS programmer needs to call just one function to display a standard dialog box that allows users to scroll through lists of files, directories, and disk drives; responds appropriately when the user clicks or double-clicks various fields and buttons within the dialog box; and returns control to the application only after the user has made an appropriate selection. Although some tasks may require calling lower-level operating system functions directly, in general the applications written for this kind of system software include more calls to application libraries than to the underlying operating system libraries.

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