These files are located under %WINDIR%\Installer\$PatchCache$ in a per-product location. This improves servicing scenarios but at the cost of additional disk space. Windows Installer 4.5 provides a feature to fix this by copying shared files to all products' baseline caches that installed those files - thus increasing disk space consumption. This can lead to source media requirements when some products are updated.
Since Windows Installer only copies a file to be updated to the baseline cache if the file will be overwritten, a baseline cache for a file might only exist for one product even if updated by a patch for multiple installed products. At most, there might be two copies of files created since Windows Installer retains a copy of the original (RTM) file and the latest minor upgrade (often distributed as "service packs") when either version of a file is initially replaced. To make either of these features possible, Windows Installer copies files to be updated to the baseline cache under %WINDIR%\Installer\$PatchCache$ for each product.
That is, if a patch were to update foo.dll v1 to foo.dll v2 using a binary delta applied to foo.dll, the patch would have to account for foo.dll v3 or even having been updated by another product installation, or the installation would fail. Windows Installer 3.0 added support to uninstall patches and to provide a more robust experience for applying binary deltas to existing files without accounting for every possible state an existing file could be in. I am curious if this is correct also why. C:Windows\Installer From what I read I should not delete this folder. We are down to about 4 free GB's due to one folder. On my Windows 2003 server we have about 50 GB on the C Drive. Baseline cache for patching and patch removal I am trying to figure out if there is a tool or if I can manually remove the contnets of this folder.