Valve has finally released the Official System Requirements for DOTA 2, and not surprisingly, they are pretty similar to Alien Swarm and Heroes of Newerth.
DotA 2 Minimum System Requirements:
* OS: Windows® 7 / Vista / Vista64 / XP
* Processor: Pentium 4 3.0GHz
* Memory: 1 GB for XP / 2GB for Vista
* Graphics: DirectX 9 compatible video card with 128 MB, Shader model 2.0. ATI X800, NVidia 6600 or better
* Hard Drive: At least 2.5 GB of free space
* Sound: DirectX 9.0c compatible sound card
DotA 2 Recommended System Requirements:
* OS: Windows® 7 / Vista / Vista64 / XP
* Processor: Intel core 2 duo 2.4GHz
* Memory: 1 GB for XP / 2GB for Vista
* Graphics: DirectX 9 compatible video card with Shader model 3.0. NVidia 7600, ATI X1600 or better
* Hard Drive: At least 2.5 GB of free space
* Sound: DirectX 9.0c compatible sound card
Subject: DOTA 2 OFFICIAL SYSTEM REQUIREMENTS 
Mon Oct 03, 2011 10:18 am
