The recent reinstallation of the Windows 7 operating system on my laptop involved a ton of updates, several of which were updates with .NET in the title.
Here’s an example of a few of them:
On reboot after installing anything with .NET in the title, Windows will crawl along very slowly as if it’s doing something very CPU-intensive in the background. And if you look at your CPU usage via the Performance tab in the Task Manager, that’s exactly what’s going on and the usage will be spiking. After that if you launch the Resource Manager, you’ll see a file called mscorsvw.exe is the guilty party eating up all the CPU cycles.
Should you spot this, it’s nothing to worry about and it’s only temporary. As it turns out, mscorsvw.exe is a .NET assembly compiler and by default will execute with high priority. Whenever .NET updates are downloaded, on next boot mscorsvw.exe does its thing in the background and compiles all the updates as fast as it possibly can.
The tradeoff to this is massive CPU usage while the compiler is running, but as you’ll read on that linked article, it’s only temporary and it will shut itself off when completed, usually in about 5 to 10 minutes.
What I find a bit funny is that the linked article is from 2005 and was obviously written for the XP operating system since Windows 7 or Vista didn’t even exist at the time, yet this exact same thing still happens now in Windows 7.
Some things never change, I guess.
Why is it helpful to know this?
If you plan on (re)installing a new copy of Windows soon, be it XP, Vista or 7, and you get to the point where all the .NET updates start coming in (which will happen), you’ll know up front why you’ll encounter a massive spike in your CPU usage on next boot, and also know that it will go away after a short while.
The CPU spiking after an update only happens with .NET updates to the best of my knowledge, so when you see one in the update list, you know what to expect.
New installations of Windows are particularly trying on the nerves because several .NET updates are required and downloaded almost all at once, all of which require auto-compiling after installation.
If you want to actually watch what mscorsvw.exe is doing – should it be running – the way to do that is to launch the Resource Monitor. In Windows 7, click the Windows logo and search for “resource”. Launch the app, and then click the “CPU” column so there’s a little arrow pointing down, which will list the highest-use resource running in the background, and will look like this:
After a .NET update and a reboot, you will see mscorsvw.exe at the top of the list, and it will be eating up a ton of cycles. As said above, it will go away once it’s done, but you may find your Windows somewhat unusable until it’s finished.
Final note: For those of you running Windows virtually, whether Windows-inside-Windows or inside OS X or Linux, yes your CPU will spike also after a .NET Windows update.
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