Pre-RTM and RTM
Build 2535 (with a build tag of 2535.xpclient.010803-1621) was released on August 8, 2001, though it offered no visual changes.
Build 2542 (with a build tag of 2542.xpclient.010811-1534) was released on August 14, 2001. It was the first build to require testers to use new types of product keys. Like the previous build, this build offered no visual changes at all. Microsoft said that this build was primarily provided to regress existing 'fixed' bugs, to uncover any last minute ship-stopper regressions, and to get a final sanity check prior to RTM.
Build 2545 was forked to Build 2600 on August 20, 2001, and the company began hammering away at this final build for RTM, alerting the press about its progress and explaining the remainder of the schedule.
Build 2600 (with a build tag of 2600.xpclient.010817-1148) On August 24, 2001, was declared as RTM, and was handed off to PC manufacturers at a media event held on the Microsoft campus.
Windows XP was released on October 25, 2001 to the general public and to retailers worldwide.
Read more about this topic: Development Of Windows XP