This tone comes from the Windows 10 Insider preview builds, where Microsoft tested new system sounds for notifications, calendar reminders and alerts before the final release. Preview builds like 10074 circulated widely among testers and tech channels, and their clean notification chimes were often ripped and reuploaded to soundboards. The calendar notify sound stuck around because it is instantly recognizable as Windows without being as overused as the error chime. Creators now use it for fake alerts, productivity jokes and retro desktop parodies.