As used in the context of software distribution a “service pack” is a collection of upgrades, updates, fixes and improvements to a particular application (or related set of applications) that are released as a single package to be installed in one go. Windows XP Service Pack 3 [SP3] was the final service pack released for Windows XP, receiving a manufacturing release on the 21st of April 2008. (It was made publicly available from the Microsoft Download Center, or via Windows Update, slightly later on the 6th of May 2008.)
It is interesting to note that Microsoft was still releasing significant Windows XP updates over a year after Windows Vista (the next version of Windows after Windows XP) had been released (to manufacturing in November of 2006 and to retail in January 2007). This may reflect XP’s ongoing popularity and the relative unpopularity of Windows Vista; a point further illustrated by the fact that Microsoft continued to sell Windows XP up until the 30th of June 2008, and not just until the 31st of January 2008 as originally intended.
There are 1,174 improvements, enhancements and fixes included in Service Pack 3, which is to say that it includes all updates for Windows XP that had been released previously, along with a number of new features. Of the previously released features most had been included in Service Pack 2 [SP2], although not all, and SP3 includes those that had been released after SP2. The advantage here, or disadvantage, depending how you look at it, is that previously you would need to choose to install each update separately, whereas they are all included in SP3 by default.
The features entirely new to Windows XP and included in SP3 are:
However SP3 specifically excludes Internet Explorer 7 or 8, so while SP3 can be installed on operating systems with Internet Explorer 6, 7 or 8 installed, and while it will implement updates to IE6 and IE7, it will not upgrade IE6 to IE7 or IE8. While this was probably done for perfectly good reasons this was, none-the-less, an untaken opportunity significantly to improve most people’s browsing experience, since IE6 has a well-deserved reputation for being a particularly poor web browser.