From Wiktionary, the free dictionary
Karte + -ei, 19th century, in analogy to words like Bücherei.
Kartei f (genitive Kartei, plural Karteien)
- card index, card catalog
Declension of Kartei [feminine]
- “Kartei” in Duden online
- “Kartei”, in Digitales Wörterbuch der deutschen Sprache[1] (in German)