If you want to find which version of Windows OS you are using, you can do that as follows.
- Click on Start button and then click on Run. (Or you can use the keyboard shortcut Win + R).
- Type Winver in the text box and then press Enter. Then you will see a window like below where you can see the Windows version and service pack number.
You can see the following text in the above window.
Version 5.1(Build 2600.xpsp_sp2_qfe.080814-1242 : Service pack 2)
This text shows that I am using Windows XP and the service pack number is 2. The text next to the windows logo in the top part indicates that I am using XP professional edition.