Knowing which Windows 7 service pack that's currently installed on your computer is valuable because you should always have installed the latest service pack available.
Some programs may require that Windows 7 is updated to a certain service pack level and may not operate correctly if that service pack is not installed.
Knowing what Windows 7 service pack you have installed can also come in handy when troubleshooting certain problems or when manually installing a service pack.
Windows 7 Service Pack 1 is the most recent service pack available for this version of Windows.
Follow the easy to follow steps below to find out what Windows 7 service pack you have:
Time Required: Determining your Windows 7 service pack level only takes a few minutes.
1. Click on Start and then Control Panel.
Tip: In a hurry? Type system in the search box after clicking the Start button. Choose System under Control Panel from the list of results and then skip to Step 4.
2. Click on the System and Security link.
Note: If you're viewing the Large icons or Small icons view of Control Panel, you won't see this link. Simply double-click on the System icon and proceed to Step 4.
3. Click on the System link.
4. In the Windows edition area of the System window you'll find your Windows 7 edition information, Microsoft's copyright information, and also the service pack level.
Take a look at the screenshot on this page for an idea of what you should see.
Note: If you don't have any service pack installed (as in my example), you won't see "Service Pack 0" or "Service Pack None" - you just won't see anything at all.
5. The latest Windows 7 service pack is Service Pack 1 (SP1).
If you find that Windows 7 SP1 is not installed, I recommend that you do so as soon as possible, via Windows Update or manually via the correct download here.
Note: Windows 7 service packs are cumulative. In other words, you only need to install the latest Windows 7 service pack available because it contains the patches and other updates for all previous service packs as well. For example, if the latest Windows 7 service pack is SP3 but you don't have any installed, you do not need to install SP1, then SP2, then SP3 - just SP3 is fine.
source: Tim Fisher