A service pack can be incremental, which means it only contains the updates that were not present in the previous service packs or, it can be cumulative, which means it includes the contents of all its predecessors. In the case of Microsoft's products, an incremental update was called a service release. For example, Office 2000 must be upgraded to service release 1 (SR-1) before one can install SP2.
Recent service packs for Microsoft Windows have not been cumulative starting with Windows XP Service Pack 3. Windows XP SP3 requires at least SP1 to be present on an installed copy of Windows XP, although slipstreaming SP3 into the gold release is still supported. An unsupported workaround to install SP3 on Windows XP RTM also exists. Windows Vista Service Pack 2 also is not cumulative and requires at least SP1 to be present on an installed copy of Windows Vista.