Based on the filename Atlas V0.5.2.iso , this appears to be a custom Windows operating system modification (often referred to as a "Windows Ameliorated" or "Gaming Tweaked" ISO). These versions are popular in the PC gaming and enthusiast communities for stripping out bloatware and telemetry to improve system performance.
Atlas typically frees approximately 1.5 GB of RAM on boot, allowing more memory to be allocated to demanding applications or games. Increased Gaming FPS: In competitive titles like Atlas V0.5.2.iso