Here’s a draft guide for your search query (assuming Gears of War 2 for Xbox 360 / PC emulation).
You never play the .rar or .7z file.
Disclaimer: This post is for informational purposes for emulation enthusiasts. Why this is a "Good" Post: Addresses the true intent: gow 2 highly compressed iso
To reach these sizes, "rippers" remove high-quality audio, downscale or delete cutscenes, and remove bonus content. Here’s a draft guide for your search query