Modern Warfare 3 System Requirements:
OS: Windows XP, Windows Vista or Windows 7
CPU: Intel® Core™ 2 Duo E6600 or AMD Phenom™ X3 8750 processor or better
RAM: 2 GB
GFX: Shader 3.0 or better 256 MB NVIDIA® GeForce™ 8600GT / ATI® Radeon™ X1950 or better
DX: 9.0c or later
HDD: 16 GB free hard drive space
INTERNET: Broadband connection and service required for Multiplayer Connectivity. Internet connection required for activation.
As we can see the requirements are not that high and gamers with older pc's have a chance to run this game and enjoy the Call of Duty experience.
SIZE = 13.7 GB