2" quad
From Tardis Wiki, the free Doctor Who reference
2" quad (also called quadruplex videotape, 2-inch quad or just quad) was the exclusive type of videotape used in the recording of Doctor Who stories from An Unearthly Child through to The Five Doctors. Several iterations were employed throughout this history, from the original 405-line black and white form, followed by its 625-line variant, and ultimately its colour renewal.
