There may be additional RBAC definitions, so PrepareAD should be executed prior to installing CU20. This will dictate if the AD Schema needs to be modified. Whether or not your AD Schema needs to be updated depends upon your initial Exchange 2013 version. Which is a great improvement over the initial CUs that all had the same file name! Details for the release are contained in KB 4055221. 003 of Exchange 2013 and the update is helpfully named Exchange2013-圆4-cu20.exe. Exchange 2013 SP1 was in effect CU4, and CU20 is the sixteenth post SP1 release. CUs are a complete installation of Exchange 2013 and can be used to install a fresh server or to update a previously installed one. Exchange 2013 CU20 has been released to the Microsoft download centre! Exchange 2013 has a different servicing strategy than Exchange 2007/2010 and utilises Cumulative Updates (CUs) rather than the Rollup Updates (RU/UR) which were used previously.