Time for a helpdesk techo blog.

Ever since upgrading to Vista, one of my machines has been plagued with the CPU running at 100% whenever I open a network folder or mapped drive.  Anytime I do this, the file folders in Explorer have a little revolving/spinning magnifying glass that will stay there until I reset the machine.  A quick review of the Windows Task Manager reveals that explorer.exe is the culprit, and it will stay at or close to 100%, making the machine virtually useless.

It seems I'm not the only person having this issue.  A quick google search on terms like "vista cpu 100%", "vista explorer.exe cpu 100%" or similar displays a huge amount of people having the problem.  At least I'm not the only one - however solutions seem to be scarce and random at best.  After searching through a lot of newsgroups, webpages, blogs and other corners of the internet to try and fix the issue, I've come up with a partial solution to recover control over an over-zealous explorer.exe.

Use this method at your own risk.

Download and install Process Explorer from Microsoft.  This product can best be described as the Windows Task Explorer on steriods.  It tells you everything your system is doing, right down the each processor thread and file that is being used.  Process Explorer was originally developed by SysInternals - a company that was later acquired by Microsoft.
http://technet.microsoft.com/en-gb/sysinternals/bb896653.aspx

When your CPU starts maxing out at 100%, fire up Process Explorer and have a look at what's happening under the hood.  As expected, it's explorer.exe that consuming 100%.  Process Explorer allows you to dig deeper into this application.  Double-click explorer.exe to have a look at all the threads it uses. 

Sort by "CSwitchDelta" and have a look at the top thread.  On my particular machine, it's a process with a "Start address" named "ntdll.dll!Rt|IntegerToUnicodeString+0x67" that is always CPU intensive thread.

I'm not exactly sure what this thread does (anyone?), but killing it restores the CPU back to a normal level immediately. 

Sometimes I get an error message a few minutes later saying "Explorer has stopped working", and after click OK, it re-starts and the machine is OK.

While I realise this isn't the most elegant way of addressing this issue, perhaps this information might give someone with a bit more knowledge about Windows processes some ideas as to why this is occuring in the first place.  There must a few helpdesk technicians out there who have run into this issue. If anyone else has some insight into the famous "Vista CPU 100%" problem, please share!

Hasta la Vista.

Rod