The Fn key existed at least as early as the PCjr, where you'd use Fn-1 to Fn-0 instead of dedicated function keys. This was also seen on some smaller laptops w

The Fn key existed at least as early as the PCjr, where you'd use Fn-1 to Fn-0 instead of dedicated function keys. This was also seen on some smaller laptops without room for dedicated function keys. (Other designs used Fn-F1 and Fn-F2 to add F11 and F12 when there wasn't room)