Memory usage is becoming more demanding as texture sizes have increased, for the newer models - 4gb is cutting it pretty close for DCS these days.
Minimum Memory requirement is 6gb
Minimum system requirements: OS 64-bit Windows Vista, 7 or 8; CPU: Core 2 Duo 2.0 GHz; RAM: 6 GB; Free hard disk space: 10 GB; Video: 512 MB RAM card, DirectX 9.0c - compatible; Sound: DirectX 9.0c - compatible; requires internet activation.
Nate