Databases are implemented via a fast three file format, and populated by importing PGN archives or other databases using the Clipbase as a cut and paste tool.
Free databases are hard to maintain. Previously we have linked to Caissabase, Kingbase and Millbase, but all have their problems. The last linked (Lumbrabase) is just too bloated really - nearly 5 million Computer Tournament games alone. Currently we have no recommendation for a decent free database.