What does the EM installer look for to determine it is an upgrade rather than a fresh installation?

Document ID : KB000095584
Last Modified Date : 11/05/2018
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When running a EM installer, (as seen on 10.5.x installer), it asks for a EM installation directory.  If this is an EM upgrade, and I enter the root directory of the existing EM instance, what does the EM installer look for to identify that this is an existing EM directory and hence will run an upgrade instead of a fresh installation? 

It looks for Introscope_Enterprise_Manager.exe first.  If Webview is installed, then it will check for webview.exe.  (same executables on Linux)

In addition, it also checks for the following files from the respective EM/Webview directory: