Installation and Patches produced by Windows Installer will keep a backup in %SystemRoot%\Installer folder for the future operation such as configuration, uninstallation and so on. This is a very good thing, but if the installation is canceled or failed, Windows Installer will not delete the MSP or MSI file before it quit. When user run the installation again, a new MSP or MSI file will copy into the %SystemRoot%\Installer folder with a new name and the previous MSP or MSI file will be useless.
There are other solutions of similar algorithm on network. If you are using the 64-bit operating system, please be sure to confirm whether these solutions support 64-bit operating system. A program does not support 64-bit operating system may delete your useful backup file in error.
After Windows Installer installed, a new key to certify the backup file will record in the registry of HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData. So we can check all the MSP and MSI files in %SystemRoot%\Installer folder whether exist in registry to get their validity. If a file is useless, we can delete it to release the disk space. Certainly, to check and delete manually is a big trouble thing. Now, we have Windows Installer Cleaner.
Windows Installer Cleaner is a free tool. It support Windows 2000/XP/2003/Vista/2008/7 operation system. It support 64-bit Windows XP/2003/Vista/2008/7 operation system, too. You can free to use, deploy and sale it. The author promise to get no fee, and does not assume any responsibility or duty.
Windows Installer Cleaner is easy to use. It check and list the useless files when startup. You can choose which to delete and which to keep. Just click Clean button to start a clean job. The clean job move the selected files to Recycle Bin, so you can restore them if neccesary.