Minimum:

Supported OS: Windows XP
Processor: 2 GHz or better Intel or AMD processor, or equivalent. Game is functional on, but currently not optimized for, Dual-core CPU's.
Memory: 512 MB of RAM
Graphics: nVidia Geforce FX with 128 MB RAM & Pixel Shader 2.0 or better, ATI Radeon 9500 with 128 MB of RAM Pixel Shader 2.0 or better
DirectX Version: DirectX 9.0c
Hard Drive: 3 GB of free space

Recommended:

Processor: 3 GHz or better Intel or AMD processor, or equivalent. Game is functional on, but currently not optimized for, Dual-core CPU's.
Memory: 1 GB of RAM
Graphics: nVidia 6800 or better with at least 256 MB of onboard RAM, ATI X800 or better with at least 256 MB of onboard RAM

ArmA: Combat Operations videos