here's a link to a White Paper from VmWare that explain the new licensing model for VmWare vSphere 5.
The new pricing introduces the concept of "Pooled vRAM Entitlement"
in the paragraph "Why a Change was Necessary" we can read:
here's the link to the complete document
With the modification to vSphere licensing, we accomplish two objectives:
• Free customers from restrictive hardware-based entitlements
• Align the vSphere licensing model with IT as a service
To understand reasons for the change, we should first examine the legacy vSphere model. vSphere 4.x is licensed on a per-physical processor (CPU) basis with limits on:
• The number of physical cores per CPU
• Physical RAM capacity per server
Significant innovations in hardware design—such as CPUs with ever-larger number of cores, high-density memory chips, solidstate drives and hyperthreading—were causing the hardware limits in vSphere 4.x licensing to become outdated. In the 36 months since the release of vSphere 4.0, multicore capacity of x86 CPUs grew from 2–4 cores per CPU to 8–12 per CPU. Processor manufacturers have announced plans to introduce CPUs that will exceed 12 cores.
CPU manufacturers have introduced or plan to introduce technologies—such as hyperthreading—that work at the subcore level and increase processing power by improving parallelization of computations. Similar growth and innovation trends are also happening on the memory side, with RAM chip density growing from 4GB per DIMM to 8GB and 16GB per DIMM and new types of memory technologies—such as solid-state-drive (SSD)—becoming mainstream. This innovation trend in server hardware technologies is rapidly making the hardware restrictions of vSphere 4.x licenses outdated posing difficulties for customers to plan future investments in infrastructure and virtualization.
Moreover, vSphere 4.x licensing did not reflect the fact that vSphere excels at pooling physical hardware resources across the entire datacenter and presenting them as a single, unified, shared infrastructure—an innovation that is one of the core pillars of cloud infrastructure. The hardware-based licensing model of vSphere 4.x made it difficult for customers to transition to the usage-based cost and chargeback models that characterize cloud computing and IT-as-a-Service.