When set, this property makes a large Windows Installer package perform a faster installation. The property can be set on the command line or in the Property table to configure operations that the user or developer determines are non-essential for the installation. The value of the MSIFASTINSTALL property can be a combination of the following values. It is available only in Windows Installer 5.0 and later.
Alex Verboon has tested this property (MSIFASTINSTALL) with a couple of installers and shared his results on how this property helped in reducing the installation time on Windows 7.
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About the Author: Vijay is a passionate Technology Evangelist and a Microsoft MVP in Application Setup / Deployment. 
