A collection of patches, fixes, and minor upgrades for a specific version of a product such as a Microsoft Windows operating system or a Microsoft BackOffice server product. A service pack is not the same as a decimal release, such as an upgrade from version 4.0 to version 4.01.
Service packs are typically identified with a number, such as Service Pack 2. Occasionally, interim releases of service packs are also issued, such as Service Pack 2a (SP2a) for Microsoft Transaction Server (MTS).
Service packs for each product are generally cumulative. For example, if you apply Service Pack 3 to a product, you normally don’t have to apply Service Packs 1 and 2 first, because Service Pack 3 includes the fixes and upgrades in Service Packs 1 and 2.
Service packs are included in Microsoft Developer Network (MSDN) TechNet subscriptions; they are also often available for download from the Microsoft Web site.
Microsoft Office service packs are known as service releases and are numbered SR-n.
Check MSDN and TechNet for a list of current service packs and what they do for each product. Before you apply a service pack, read its documentation to determine whether you need to apply it. Occasionally, service packs must be applied in a specific order on a system that is running more than one BackOffice product. Check MSDN, TechNet, or the Microsoft Knowledge Base for information on this kind of situation.
Service packs often include new features or additional optional components for the product, in addition to bug fixes and patches. A common misconception about service packs is that while they are cumulative with respect to bug fixes and patches, they might not be cumulative with respect to new features or components. For example, Service Pack 4 for Windows NT 4.0 includes Microsoft Windows Media Player, but Service Pack 5 for Windows NT 4.0 does not include this new utility. So if you simply want to patch your product against bugs, you need only apply the most recent service pack for the product. But if you want to make use of product enhancements and new features, you might need to apply each of the service packs for the product in succession.