A small but mighty fix. Older routers sometimes failed to send "Packet Too Big" messages. SP3 added detection for these "black hole" routers, preventing random web page timeouts.
Today, SP3 is a museum piece. But for those who lived through it, the sound of the startup chime, the green rolling hills of "Bliss," and the stability of a properly tuned SP3 machine are the stuff of computing legend. Microsoft Windows XP SP3
Though Microsoft ended official support in 2014, XP SP3 remains a milestone for several reasons: Windows XP SP3 review - Tech Advisor A small but mighty fix