Below are the minimum and recommended system requirements.

Minimum System Requirements for Mass Effect on the PC

Operating System:
Windows XP or Vista

Processor:
2.4+GHZ Intel or 2.0+GHZ AMD

Memory:
1 Gigabyte Ram (XP)
2 Gigabyte Ram (Vista)

Video Card:
NVIDIA GeForce 6 series(6800GT or better)
ATI 1300XT or better (X1550, X1600 Pro and HD2400 are below minimum system requirements)

Hard Drive Space:
12 Gigabytes

Sound Card:
DirectX 9.0c compatible sound card and drivers

Recommended System Requirements for Mass Effect on the PC

Operating System:
Windows XP or Vista

Processor:
2.6+GHZ Intel or 2.4+GHZ AMD

Memory:
2 Gigabyte Ram

Video Card:
NVIDIA GeForce 7900 GTX or higher.
ATI X1800 XL series or higher

Hard Drive Space:
12 Gigabytes

Sound Card:
DirectX 9.0c compatible sound card and drivers – 5.1 sound card recommended