Operating System

The operating system (OS) serves as an interface between the user and the computer hardware. The OS manages the computer's activities and resources, without the user needing to understand the computer's inner workings. Other computer applications run inside the OS, which manages hardware access for the applications. All computers use an operating system – personal computers, hand held computers such as iPhones, and even gaming/entertainment consoles like the Playstation 3, Xbox 360, and Wii. Some devices use an embedded OS, rather than one a user installs such as on a PC.

OS's provide many services to applications and computer users. The applications utilize these services through an API (application programming interface) or through system calls. Applications request the service, pass instructions, and receive the results. Users interact with the OS through a UI. In the early days of DOS and Unix users typed commands on a command line, but modern computers use a GUI (gooey) interface for easier communication between user and computer. Some OS's include the user interface, some communicate with the user through an application executed aside from the OS.

The configuration of a computer system with an OS follows the same basic path for all types of OS's and hardware:

User -->UI-->OS

Application -->OS-->Hardware

Current operating systems include:

Various forms of Microsoft Windows (XP, Vista, Windows 7)
Various forms of Mac OS
Various types of Linux including Red Hat
BSD
Solaris

Microsoft Windows maintains the largest share of the PC (desktop and notebook) market, while Unix or Unix-like OS's lead the way in servers. Embedded devices such as cell phones and iPods use a variety of OS's – no one has emerged dominant.

OS's work through a variety of functions, including:

Interrupts - OS's interact with the computer environment through interrupts, a less CPU intensive method than watching inputs known as polling. CPUs directly support interrupt programming. Through interrupts, the OS (computer) launches code in response to events. Programs or computer hardware trigger interrupts. The OS determines how to deal with the interrupt, running a code in a certain order or priority depending on the interrupt priority. For example a person (his brain the OS) decides to run out of the house instead of answer the phone when both the fire alarm and phone ringer sound.
Protected mode and Supervisor mode – The OS manages which programs have unlimited access to the CPU (supervisor mode) and which access only limited resources (protected mode.)
Memory Management – The OS ensures that programs don't interfere with other programs' memory use.
Virtual Memory – The OS manages swapping data from temporary disk storage to storage in main memory as different programs call for memory use.
Multitasking – The OS manages programs' access to computer resources so they appear to run at the same time.
Device Drivers – Device drivers allow access to various hardware devices through the OS.
Security – The OS differentiates between allowed requests and disallowed requests such as those made by malware and viruses both inside the computer and connected to the computer via a network.