VMware has a free version of vSphere available called vSphere Hypervisor. This is meant for home labs, testing and education. The main goal is get people who are not familiar with virtualization get experience with it. For production vSphere Essentials kits or the various editions should be used.
Version 4 could be used with an unlimited number of internal memory assigned to virtual machines. It is limited in for instance remote management and backup’s/provisioning.
vSphere Hypervisor will have a limit of 32 GB of physical RAM. It is very well possible to run virtual machines with a total configured memory of 32GB (memory overcommit). So there is no vRAM for the free ESXi 5.