Service pack

A service pack (in short SP) is a collection of updates, fixes and/or enhancements to computer software, delivered in the form of a single installable package. Many companies, such as Microsoft or Autodesk, typically release a service pack when the number of individual patches to a given program reaches a certain (arbitrary) limit. Installing a service pack is easier and less error-prone than installing a high number of patches individually, even more so when updating multiple computers over a network.

Service packs are usually numbered, and thus shortly referred to as SP1, SP2, SP3 etc. They may also bring, besides bug fixes, entirely new features, as is the case of SP2 of Windows XP.

Incremental and cumulative SPs
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.

Impact on installation of additional software components
Application service packs replace existing files with updated versions that typically fix bugs or close security holes. If, at a later time, additional components are added to the software using the original media, there is a risk of accidentally mixing older and updated components. Depending on the operating system and deployment methods, it may then be necessary to manually reinstall the service pack after each such change to the software. This was for example necessary for Windows NT service packs, but from Windows 2000 onwards, Microsoft implemented a deployment strategy to prevent this. (setup programs are redirected to use updated service pack files, instead of files from original installation media, where necessary)