Windows Whistler was Microsoft's codename for the operating system released as Windows XP in 2001, and its logon sound was heard during test builds and the first-run setup process. Unlike the final XP startup sound, this version stayed mostly known through beta archives, installation videos, and system sound collections shared online. It remains popular with retro computing fans who compare prototype sounds to final releases, often alongside the classic Windows error sound in compilations exploring how the interface evolved before launch.