IMPORTANT: Install this AFTER you've installed the main files!
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Very Low-End = lowest quality, best performance.
Low-End = low quality, good performance.
Mid-End = medium quality, medium performance.
High-End = high quality, lower performance.
Ultra-End = highest quality, lowest performance.
Insane-End = Insane quality, only for insane PC's.

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Installation:
Copy the files inside one of the folders to your GTA IV main folder.