Common Hardware & Software Resources Managed by Operating Systems

The operating system (OS) manages at least one processor. The processor (or CPU) is the electronic chip that performs that actual work of executing a process, such as running a web browser or playing music in an MP3 player. The operating system determines when and how much time each process gets "in the processor." The operating system switches between running processes quickly enough to give the illusion that the processes are executing simultaneously. In the case of multiprocessor or multicore systems, the OS also manages which processor or core executes a process.

Every modern computer system has memory, and all processes exist in memory until the computer system is turned off. The operating system manages how much memory each process gets to use for itself and its data. Every time a word processor opens another document or a Web browser displays another page, the program requests memory from the operating system. If there is still memory available, the operating system grants the request and tells the requesting program which portion of memory it can use. If no memory is left, it refuses the request and the program has to tell the user that there is not enough memory for it to open the document or Web page.

The majority of modern computer systems have a hard drive. When a program is not running, the program itself and its data is stored on the computer's hard drive. The operating system controls where on the hard drive a program and its data is stored, provided sufficient space is available. Programs requiring more storage than the disk drive will hold receive a message from the operating system. Most programs then inform the user that there is not enough space to install the program.

The operating system controls reading from and writing to various forms of removable media. The most common example today is an optical drive, such as a CD-ROM or DVD-ROM. If the system has a floppy drive or the user is using a USB thumb drive, the OS manages all access to these devices.

The operating system controls all processes -- any running programs -- on the computer system. This includes word-processing software, Web browsers, games, device drivers and all other types of running programs. The operating system manages all of these. When the programs are invoked, the OS assigns a priority to their execution and designates how much much memory they can have.

The operating system responds to input devices such as mice, keyboards, joysticks and touch screens by notifying the foreground process (the process the computer operator is using). The foreground process then responds to the input as appropriate. With some devices, the operating system also responds; for instance, when the mouse is moved, the OS updates the mouse pointer's position on the screen.