Does ESXi 4 have the same limits as ESXi 5

I am new to the process of virtualization and was told that vsphere was a good place to start.

I just became aware that there is a memory limitation for vsphere 5, does this also apply to ESXi4? I am needing to know if I can download ESXi 4 without limits (or maybe there are limits that I am not aware of), otherwise, I will have to consider vsphere 5 and purchasing the Essentials package. Trying to weigh my options.

I apologize if this has been asked already, please direct me to thread if it has.

Thanks