1.2 Operating Systems (OSes)

An operating system is a piece of software the provides a common interface to access resources for application programs. Examples of application programs include Mozilla Firefox, Microsoft Internet Explorer, Macromedia Dreamweaver, Microsoft Access, the GIMP, Adobe Acrobat Reader, and etc.

Depending on the context, the resources under the management of an operating system varies. Most operating systems manage the following resources:

• Memory. An application program can request more memory, or deallocate memory with an operating system.
• Processing resources. The processing capacity of a processor is allocated to individual processes (programs in execution).
• Storage resources and files. An application can request the creation, deletion and modification of files and directories.
• Console. An application can communicate with a user via the console.
• Graphical User Interface (GUI) . An application program can request operations related to the GUI.
• User input. An application program can request that the OS sends user input events to it.

Without an operating system, application programs need to manage low-level services by themselves. Not only is this cumbersome, but it is also very dangerous. With an operating system in place, programs are (somewhat) protected from each other. In other words, it is difficult for one program to crash the entire system, or for one program to use up all the resources.