Windows is the name of Computer Operating System build and marketed by Microsoft Inc. Windows OS also runs in servers, tablets and mobiles. It’s proprietary software.
The Windows Operating System is proprietary software program developed and distributed by Microsoft Inc. to run in Home PC, Office Computers, Servers, Tablets and Smartphones. The Windows Operating System or Windows OS as it's popularly called powers 90% home and office computers worldwide. It has many variants, the latest is Windows 8; however, very soon we will see Windows 10 running in PCs, Mobiles and Servers. Among most successful Windows OS was Windows XP, in fact most loved OS till date. But for many technological and business reasons Microsoft has completely removed Windows XP including support from its stores.