So I just installed RU1 on my brand new Exchange 2010 server and then I issue a Get-Exchangeserver -Identity MyExchangeServer and get the following output for AdminsDisplayVersion and ExchangeVersion:
Ok that looks a little familiar for some reason. I go to my Exchange 2010 RTM server and issue the same cmdlet and get:
...The same result! But one server has RU 1 installed and the other is RTM. Shouldn't I get a different version number back?
Well... no. Exchange 2007 and forward do not reflect the version number either in the value for AdminDisplayVersion, ExchangeVersion, or at this registry key HKLM\SOFTWARE\Microsoft\v8.0\<Role>\ConfiguredVersion as influenced by roll ups. This is a common misconception.
The most conclusive way to get the version of your exchange server, rollup and all, is to check the file version of ExSetup.exe in the BIN folder.
Here is Exchange 2010 RU1 version:
And here is Exchange 2010 RTM:
Another way of getting this information is to run the following PowerShell one-liner:
GCM exsetup |%{$_.Fileversioninfo}
The below output is from an exchange 2010 server running RU1:
Here is an exchange 2010 RTM server:
You can then correlate the version number you find with those listed in Exchange Server 2007: Platforms, Editions, and Versions, Build numbers and release dates for Exchange Server or on the actual rollup update download pages.
Hope this post reduces some confusion out there!