• File and folder management – An operating system creates a file structure on the computer hard drive where the user data can be stored and retrieved. When a file is saved, the operating system saves it, attaches a name to it, and remembers where it put the file in the hard drive for future use.
• Management of applications – When a user requests a program, the operating system locates the application and loads it into the primary memory or RAM of the computer. As more programs are loaded, it is the job of the operating system to allocate the resources of the computer. 
• Support for built-in utility programs – Utility programs are programs that the OS uses to maintain and repair itself. These programs help identify problems, locate lost files, repair damaged files, and backup data. In Figure , the Defrag utility program is running in the Windows OS. It is checking the hard drive for lost files and other problems.
• Access control to computer hardware – The OS sits between the programs and the Basic Input/Output System (BIOS). The BIOS was explained in previous chapters and more will be provided later in this chapter. The BIOS does the actual hardware control. All programs that need hardware resources must first go through the operating system. The OS in turn can either access the hardware through the BIOS or through the device drivers (discussed in Chapter 5). Windows 2000 NOS bypasses the system BIOS and controls the hardware directly.

All programs are written for a specific operating system. Programs written for the UNIX operating system will not work on a Windows-based system, and vice versa. The OS relieves the programmer of having to consider hardware access when writing an application. If the operating system did not communicate information between the application and the hardware, programs would have to be rewritten every time they were installed on a new computer.