First up, the PC tech specs, which are specifically for the demo but shouldn't be much different from that of the final game:
Minimum Spec:
CPU - 1.8 GHz Intel Core 2 Duo (equivalent AMD CPU)
RAM - 1GB for XP / 2GB RAM for Vista/Win 7
Disc Drive - 1x speed
Hard Drive - 15 GB of free space
Video - 256 MB* (with Pixel Shader 3.0 support)
Sound - DirectX 9.0c compatible
DirectX - DirectX 9.0c August 2009 (included)
Recommended Spec:
OS - Windows XP SP3/Vista SP1, Win 7
CPU - 2.4 GHz Intel Core 2 Duo (equivalent AMD CPU)
RAM - 2GB for XP / 4GB RAM for Vista/Win 7
Disc Drive - 1x speed
Hard Drive - 15 GB of free space
Video - AMD/ATI Radeon HD 4850 512 MB or greater, NVidia GeForce 9800 GT 512 MB or greater
Sound - DirectX 9.0c compatible
The developer goes on to confirm the contents of the demo. It will contain both single- and multiplayer modes.
The single-player options serves up "roughly 1 to 2 hours of content" in two areas; "The opening level featuring the Reaper attack on Earth, and a level further into the game where Shepard travels to an alien home world to seek their assistance in the war effort", explains BioWare.
The co-op multiplayer portion gives you two maps, Slum and Noveria, and opens to all players on February 17. However, those who own Battlefield 3 and have activated BF3's Online Pass code will gain early access to this mode on February 14 by logging in with the same EA Origin account.
More details are in a Q&A through the source link.
http://www.computerandvideogames.com/332714/mass-effect-3-pc-specs-revealed/