Hardware requisites for a three-node cluster topology can only be found in this page:
https://docs.openshift.com/container-platform/4.14/installing/installing_with_agent_based_installer/preparing-to-install-with-agent-based-installer.html#recommended-resources-for-topologies

While the three-node cluster (a.k.a. compact cluster) can be deployed on different platform like vsphere, baremetal, etc... 

OCP 4.12, 4.13, 4.14, 4.15    

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Hard to find (non-intuitive) way to actually find the hardware requisites

We should have a clear view of the minimum and recommended requisites for the different topologies (not only the three-node cluster) available on each of the installation options. A link to a common place with all the requisites for all options could be a good option (no duplication of data)