In the same way Ford and other vehicle manufacturers send out recalls for you to return your SUV or coupe to get a part replaced, does WSUS return to Microsoft for a patch, a fix, a service pack or a new function for your computer? The big difference between cars and Windows is that you don't have to take your software back to the store you bought it from every time it croaks. Without WSUS, you'd be going back to the software store at least twice a week; and with the price of gas, we would all go broke.
Of course, being connected to the Internet is a risky business and you need a way to quickly update your servers and desktops before the next tsunami of hostile bits comes bearing down over your DSL lines and cable connections. In fact, Microsoft touts WSUS as "the way to get secure, and stay secure." It's fast, easy to use and clean. In short, it's the software version of Windex in a bottle.
What It Does
So what does WSUS do? For the most part, it does exactly what SUS does, and then some. It connects to Microsoft, gets a catalog of updates and patches that need application to your machines, and then lets you manually or automatically (unattended) update and patch at your will. WSUS, however, goes a lot further with respect to the products it patches. Like SUS, it patches and updates all Windows 2000 and Windows 2003 Server and Desktop products, but it can also patch server and desktop applications, such as SQL Server, Exchange Server and Microsoft Office. It can also technically update non-Microsoft products that are installed on the Windows operating systems.
The products that can currently be updated by WSUS include Office XP, Office 2003, SQL Server 2000 and Exchange 2003; it's likely that when SQL Server 2005 is released in November, it too will support WSUS. More products will be added to the WSUS-compliant list as Microsoft extends them to support WSUS; you will not need to upgrade or redeploy WSUS when the additional applications announce support for it.