Unlocked multiplier means that if your motherboard has multiplier adjustments in the bios, you can set your multiplier (within a specific range, such as 10.0-13) by simply changing the setting in the bios. Locked multiplier means that you can only change the fsb setting for overclocking, unless you modify your athlon, which voids the warranty. P4's are all locked, except for the ocassional rare engineering sample, which few people ever see. The second statement implies that all athlon xps have about the same maximum potential for overclocking. The ceiling is about 2400-2500, which is a good average. The barton 2500 is a classic overclocking cpu. All you have to do is change the fsb from 166 to 200, and with pc3200, many (but not all) will run perfectly stable with little or no voltage increase, and post as an xp3200.