I know about debugging symbols (PDBs), the MS Symbol Server and the caching of symbols.
What I do not get is which symbols (by whom) go into the C:\Windows\Symbols\dll directory. It doesn't seem C:\Windows\Symbols\dll has anything to do with MSSS caching.
Example, my version of this directory contains:
C:\Windows\Symbols\dll>dir
21.02.2013 16:47 <DIR> .
21.02.2013 16:47 <DIR> ..
18.02.2011 16:18 3.854.336 atl100.i386.pdb
18.02.2011 18:23 25.300.992 mfc100.i386.pdb
18.02.2011 18:22 28.938.240 mfc100d.i386.pdb
18.02.2011 18:23 25.473.024 mfc100u.i386.pdb
18.02.2011 18:23 29.241.344 mfc100ud.i386.pdb
18.02.2011 18:26 4.386.816 mfcm100.i386.pdb
18.02.2011 18:26 4.452.352 mfcm100d.i386.pdb
18.02.2011 18:26 4.403.200 mfcm100u.i386.pdb
18.02.2011 18:26 4.468.736 mfcm100ud.i386.pdb
18.02.2011 18:05 13.824 Microsoft.Workflow.ExpressionEvaluation.pdb
18.02.2011 16:18 3.755.008 msvcp100.i386.pdb
18.02.2011 16:18 4.377.600 msvcp100d.i386.pdb
18.02.2011 16:17 8.875.008 msvcr100.i386.pdb
18.02.2011 16:18 7.900.160 msvcr100d.i386.pdb
18.02.2011 18:26 1.699.840 vcomp100.i386.pdb
18.02.2011 18:26 1.798.144 vcomp100d.i386.pdb
But no other files, although this machine has both VS2005 and VS2010 installed. I always thought the files get put there by VS, but since the ...80... versions are missing (which I have on other machines), it seems VS2005 didn't put them there.
These are pdbs that help you step through the MFC code. This is being put in here by VS and more specifically the VC++ installation which would be a part of your VS install.