Whistler was Microsoft's development codename for the system released as Windows XP in 2001, following test builds that circulated during 2000 and 2001. Enthusiasts and beta testers shared those early builds, preserving their startup screens, logos and sounds long after the final version replaced them. The welcome animation clip survives as a piece of that pre-release history, and retro computing channels still reuse it to set a scene, identify an era at a glance, or contrast early interface design with modern Windows.