I could be mistaken, but I believe SP3 is cumulative and contains whatever fixes are included in SP2. Installing SP3 requires at least SP1a
as a prerequisite >>> (among other things). <<< very useful KB950717Windows XP Wiki Service Packs: http://en.wikipedia.org/wiki/Windows_XP#Service_packs
>>>Microsoft occasionally releases service packs for its Windows operating systems to fix problems and add features. Each service pack is a superset of all previous service packs and patches so that only the latest service pack needs to be installed, and also includes new revisions. However if you still have the earliest version of Windows XP on Retail CD (without any service packs included), you will need to install SP1a or SP2, before SP3 can be installed.
Older service packs need not be manually removed before application of the most recent one. Windows Update "normally" takes care of automatically removing unnecessary files.<<<
In other words, you'd only need to install more than 1 service pack if you are updating an XP installation without at least SP1a.
Edited by Union_Thug, 19 February 2012 - 10:46 PM.