Kdb+ uses Lambda architecture has the following properties:
Data currently using stores in memory, while historical data is stored on disk.
New data come in from streaming sources.
Event-engine distribute data to downstream subscribers, including real-time database engine and streaming query engine.
Real-time database projects its content down to on-disk historical database for analytic use at daily basis, controlled by event-engine.
Decomposition Storage Model (Columnar)
Kdb+ uses DSM both for in-memory and on-disk storage.