David Ducolon on the Microsoft Office 2007 Project blog posted an article entitled Confusion – what is a CU or an IU versus a SP??? I put the following together to help me and our system administrators better understand the difference between a CU, IU, and SP.
Microsoft recently began releasing Cumulative Updates (CU) and Infrastructure Updates (IU) in addition to Service Packs (SP). CUs and IUs are currently focused on Microsoft Windows SharePoint Services and Microsoft Office infrastructure products such as Microsoft Office SharePoint Server (MOSS), Project Server 2007, and PerformancePoint.
A CU is a grouped set of Hotfixes. When a CU releases, customers will only be given the patch if they already have an open service request that is fixed with the CU or if they specifically request the Hotfix patch.
A SP is a roll-up of Hotfixes with some strategic improvements from the engineering team.
An IU is not just bug fixes but also core changes to the product with highly anticipated customer experience improvements. The IU was a hybrid of the above. An IU patch can contain changes to Infrastructure code that other applications rely upon. For more information on the recent IUs, see http://support.microsoft.com/kb/951695/, http://support.microsoft.com/kb/951297, and http://blogs.msdn.com/sharepoint/archive/2008/07/15/announcing-availability-of-infrastructure-updates.aspx.
I think I got it right.