The NVIDIA nForce2 400 Memory Controller is a chipset component that is part of the NVIDIA nForce2 series of chipsets, which were used primarily on motherboards with AMD Athlon XP processors. The Memory Controller is responsible for managing the communication between the CPU and the system's RAM (memory), facilitating the reading and writing of data. The NVIDIA nForce2 400 chipset, specifically, offers support for DDR memory, and the Memory Controller driver enables proper interaction between the motherboard, memory modules, and the operating system.