portal 2

Minimum System Requirements:

CPU: 3.0 GHz P4, Dual Core 2.0 (or higher) or AMD64X2 (or higher)
RAM: 1GB XP / 2GB Vista
VGA: Video card must be 128 MB or more and should be a DirectX 9-compatible with support for Pixel Shader 2.0b (ATI Radeon X800 or higher / NVIDIA GeForce 7600 or higher / Intel HD Graphics 2000 or higher).
DX: DirectX 9.0c compatible
OS: Windows 7 / Vista / XP

http://gamesystemrequirements.com/

HDD: At least 7.6 GB of Space

Note: Mac System Requirements o OS: MAC OS X 10.6.6 or higher o Processor: Intel Core Duo Processor (2GHz or better) o Memory: 2GB o Hard Disk Space: At least 7.6 GB of Space o Video: ATI Radeon 2400 or higher / NVIDIA 8600M or higher