The 4008 and 4009 were designed, as a pair, to simplify interfacing the 4004 with standard
RAM and ROM devices, like the C2102A (RAM) and C1702A (EPROM). Prior to the
4008/4009, interfacing the 4004 to standard RAMs and ROMs (those other than the 4001
and 4002) was a difficult task that required significant wiring and multiple IC's.

The 4009 was available in the white ceramic ( C ) package, the brown ceramic ( D ) package and the plastic ( P ) package with gold or silver legs.