|"what is perflib_perfdata_ with various exten" (sions)|
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Apparently they are created when you boot the computer and load Windows, you can't delete them, they are deleted automatically when you Shut Down Windows,and new ones are made the next time you boot the computer and load Windows
Why do you want to delete them ?
A search of my XP system shows they are only 16kb each in size.
There would be no point to deleting them since they're deleted when you Shut Down Windows in any case.
If you're trying to delete the entire contents of C:\Windows\Temp, that can't be done, unless you access the drive from another operating system (as in, you are not loading the same Windows installation).
Windows always has made files there that are being used.
Otherwise, the deleting of the files progress will halt when it encounters the first file that is being used by Windows and produces an error message.
There are things you can do in Windows to delete temporary files that are not being used without you getting the deleting progress halting,
e.g. Control Panel - Classic view - Internet Options - delete Temporary Internet files etc.,
and there are lots of third party programs that can get rid of things that those things you can do in Windows won't get rid of.