The 400MB version is not an official release. Rockstar Games has never published a version of the full game smaller than a DVD’s capacity (4.7GB).
Since this is based on the classic version, the requirements are very low: Windows 7/8/10/11 CPU: Pentium 3 or Athlon equivalent (1.0 GHz) RAM: 256 MB (though 512 MB+ is recommended) gta san 400mb pc