Every license edition of vSphere 5.0 entitles a certain amount of vRAM.
* Note: this limit is GB of physical RAM per physical server
vRAM vRAM is a licensing-specific measure for the memory that is configured for powered-on virtual machines that run on ESXi 5.0 hosts. vSphere 5.0 license keys have per-processor capacity with pooled vRAM entitlements. When you assign a vSphere 5.0 license key of a certain edition to an ESXi 5.0 host, the key adds a certain amount of vRAM to a vRAM pool that is created for the corresponding license edition.
For example, if you license an ESXi 5.0 host with vSphere Standard, a vRAM pool for vSphere Standard is created.
The amount of vRAM that a vSphere 5.0 key adds to a vRAM pool is equal to the processor capacity of the license key multiplied by the vRAM entitlement for license edition.
For example, if you license an ESXi 5.0 host with vSphere Standard key for five processors and 32GB of entitled vRAM, the amount vRAM that the key adds to the pool for vSphere Standard is 160GB. (5 processor X 32 GB RAM = 160)
For example, if you power on a new virtual machine on an ESXi 5.0 host that is licensed with vSphere Standard and configure 6GB of memory to the machine, 6GB of vRAM is consumed from the vRAM pool for vSphere Standard.
A vRAM pool aggregates all vRAM entitlements of vSphere 5.0 license keys of one edition that are assigned to ESXi 5.0 hosts. A vRAM pool for one license edition is available for one vCenter Server or a Linked Mode group. The amount of vRAM that is available in a vRAM pool for a license edition determines the total amount of memory that you can provision on powered-on virtual machines running on ESXi 5.0 hosts.
For example, you assign license key A of vSphere Standard to an ESXi 5.0 host. The key has a capacity of six processors and entitles 32GB of vRAM. The vRAM pool that is created for vSphere Standard contains 192GB (32 X 6 Processor) of vRAM that license key A provides. Later, you assign license key B of vSphere Standard to another ESXi 5.0 host. License key B has a capacity for 10 processors and entitles 32GB of vRAM. License key B adds 320GB (32 X 10) of vRAM to the vRAM pool for vSphere Standard. The total amount of vRAM that is available in the vRAM pool for vSphere Standard is the sum from the vRAM entitlements of license key A and license key B, that is 512GB (320 + 192) . In this example, you can provision up to 512GB of memory on the virtual machines that run on the ESXi 5.0 hosts that are licensed with vSphere Standard license keys.
If you assign vSphere 5.0 license keys of different editions to ESXi 5.0 hosts, a separate vRAM pool is created for every license edition.
For example, suppose that you assign vSphere Enterprise to a certain group of ESXi 5.0 hosts and vSphere Standard to another group of ESXi 5.0 hosts. As a result, two vRAM pools are created, one for vSphere Standard and another for vSphere Enterprise.