Some encoders use extreme compression algorithms to shrink game files. However, shrinking 25GB down to 400MB is nearly impossible without removing 90% of the game's content (like all audio and cutscenes).

Files labeled as "400MB" are often one of three things:

Even highly compressed "repacks" from well-known groups like FitGirl Repacks typically weigh in at around 11.3 GB . Operating System: Windows 7 (x64) or higher. Memory: Minimum 4 GB RAM (8 GB recommended).