You'll want to list your CPU, RAM, Graphics, Operating System, and possibly if you have an Solid State Drive, or normal HDD.
The minium specs on ARMA 2 are as follows:
Dual Core CPU (Intel Pentium 4 3.0 GHz, Intel Core 2.0 GHz, AMD Athlon 3200+ or faster)
1 GB RAM
GPU (Nvidia Geforce 7800 / ATI Radeon 1800 or faster) with Shader Model 3 and 256 MB VRAM
Windows XP
10 GB free HDD space
The recommended specs are as follows:
Quad Core CPU or Dual Core CPU (Intel Core 2.8 GHz, AMD Athlon 64 X2 4400+ or faster)
2 GB RAM
GPU (Nvidia Geforce 8800GT / ATI Radeon 4850 or faster) with Shader Model 3 and 512 MB VRAM
Windows XP or Windows Vista
DVD (Dual Layer compatible)
10 GB free HDD space