PC requirements

Arma 2: Combined Operations System Requirements

Arma 2: Combined Operations needs at least 2 GHz or better Intel or AMD processor, or equivalent. Game is functional on, but currently not optimized for, Dual-core CPU's., 512 MB of RAM and 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 graphics.

Verified Sources: Steam store listing
Arma 2: Combined Operations minimum and recommended PC specifications
Component Minimum
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
Storage 3 GB of free space
Not sure how your PC compares? Use the Can I Run It checker — pick your CPU and GPU and it tells you which column you land in.

Other platforms

Arma 2: Combined Operations is also available on these systems, where hardware is fixed and no per-PC check is needed:

Quick answers

Running Arma 2: Combined Operations on PC

Can my PC run Arma 2: Combined Operations?
Compare your CPU, GPU and RAM against the minimum column below. If your parts match or beat every minimum row, the game will launch — though you may need to lower settings. Matching the recommended column is what gets you 60fps at 1080p.
How much storage does Arma 2: Combined Operations need?
3 GB of free space