What is svchost.exe And Why Is It Running?

What is svchost.exe And Why Is It Running?
You are no doubt reading this article because you are wondering why on earth there are nearly a dozen processes running with the name svchost.exe. You can't kill them, and you don't remember starting them… so what are they?
So What Is It?
According to Microsoft: "svchost.exe is a generic host process name for services that run from dynamic-link libraries". Could we have that in english please?
Some time ago, Microsoft started moving all of the functionality from internal Windows services into .dll files instead of .exe files. From a programming perspective this makes more sense for reusability… but the problem is that you can't launch a .dll file directly from Windows, it has to be loaded up from a running executable (.exe). Thus the svchost.exe process was born.
Why Are There So Many svchost.exes Running?
If you've ever taken a look at the Services section in control panel you might notice that there are a Lot of services required by Windows. If every single service ran under a single svchost.exe instance, a failure in one might bring down all of Windows… so they are separated out.
Those services are organized into logical groups, and then a single svchost.exe instance is created for each group. For instance, one svchost.exe instance runs the 3 services related to the firewall. Another svchost.exe instance might run all the services related to the user interface, and so on.
So What Can I Do About It?
You can trim down unneeded services by disabling or stopping the services that don't absolutely need to be running. Additionally, if you are noticing very heavy CPU usage on a single svchost.exe instance you can restart the services running under that instance.