Which Windows version was the first to require product activation?

Windows XP was the first Windows version to require product activation for its standard non-enterprise licenses. Microsoft introduced the system to reduce unauthorized copying by tying an installation to a product key and a hardware-based installation ID.

After installation, retail and system-builder copies generally had to be activated within 30 days, either online or by telephone. If activation did not occur during the grace period, Windows XP restricted normal use until the process was completed. Significant hardware changes could also trigger a request for reactivation.

The requirement did not apply identically to every licensing channel. Windows XP volume-license editions were designed for organizations and did not use the same activation process. Large original-equipment manufacturers could also use BIOS-based mechanisms rather than the retail activation flow.

Product activation was not invented for Windows XP: Microsoft had already used activation in selected editions of Office and Word. XP was nevertheless the first major Windows release to make activation a standard part of its consumer licensing model. Later Windows versions continued and expanded the system.