An operating system (OS) is the oxygen to a computer.
An operating system is a combination of different kinds of programs and data, which runs a computer.
It manages the computer hardware and ensures the ability of performing a task for different kinds of programs and applications.
OSs can be classified in various ways- according to their kernel types, file systems, performance, security systems etc.
Real-time OS: These types of OSs are designed for running real-time applications.
They usually allow running multiple operations at a time.
Multi-user and Single-user OS: If more than one user can perform different operations at a time with their own user-accounts, it is a Multi-tasking OS.
When only one user can perform operations at a time it is Single-user OS.
Multi-tasking and Single-tasking OS: If only a single program is allowed to run at a time, is called Single-tasking OS; otherwise that is Multi-tasking.
Distributed OS: An operating system which manages a group of independent computers and makes them work like a single computer is known as a distributed OS.
Embedded System: The OSs designed for being used in embedded computer systems GNU, BSD, UNIX, Minix, OSKDE, MS-DOS, OS/2, OS-x, SunOS are some Predecessors on which some great Operating Systems have been developed.
Today, some of the greatest and popular OSs are Windows XP, Windows Vista, Windows 7, Ubuntu-Linux, Kubuntu-Linux, Fedorra-Linux, RedHat-Linux, Mac, OpenBSD, FreeBSD, NetBSD, SunSolaris etc.
There is another form of OS- WebOS or Web operating system.
Some popular WebOSs are EyeOs iCloud CorneliOS myGoya Cloudo.