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VMWare vsphere standard Acceleration KIT
Each kit consists of six processor licenses for vSphere and a license for one instance of vCenter Server Standard.
vSphere Acceleration Kits decompose into their individual kit components after purchase. This allows customers to upgrade and renew SnS for each individual component on its own schedule.
VMWare and Essential Plus Kit
Each kit consists of six processor licenses for vSphere and a license for one instance of vCenterServer for Essentials. Scalability limits for the kits are product-enforced and cannot be extende do ther than by upgrading the whole kit to an Acceleration Kit
The vCenter Server Essentials is limited and can only manage up to 3 servers with 2 PCUs each.
In general all licenses are sold with a support contract and software subscription.
More information and details in the following link: