Ragnarok Zero: Global is distributed through the official GNJOY site. The official download page lists a full client installer and says Ragnarok Online Zero needs more than 5 GB free disk space for installation, with 8 GB or more free HDD space as the minimum storage line and 10 GB or more SSD space recommended.
The official requirements are light by modern standards: Windows 10 32/64-bit, Pentium4 3.0G or Athlon64 3700+ minimum, 1 GB RAM minimum, and D3D graphics with 64 MB VRAM minimum. Recommended specs move to Intel i3-530 or Athlon64 x2 6000+, 8 GB RAM and 1 GB VRAM.
The important commercial point is subscription access. That is the fairness promise, but it also means the install is not the same low-friction funnel as a free Steam MMO.