VMware announced that they will begin support for running ESX on a single physical, multi-core (up to 4) processor.
Previously, the VMware end user license agreement was unclear about whether this was supported, creating much debate over this subject in the VMware forums (see ESX Pricing and VMware Planning). Customers were getting different responses from VMware with some representatives saying it was OK to do this and others saying it was not. One response from VMware on this issue was that it technically would work but that it was not officially supported.
Despite recent support, ESX is only being sold in two CPU increments while only being supported if a physical server is in on the VMware approved Hardware Compatibility List (HCL). This can be advantageous to customers who want to buy lower cost servers with a single processor and use them for less intensive applications. It also allows for smaller customers to buy two single processor, multi-core servers and split a ESX license between them, taking advantage of redundant hardware and features like High Availability and vMotion.
It’s good to see VMware changing their licensing policies to better adapt to customers needs. Multi-core processors have caused many other vendors to change their licensing policies to be more restrictive but VMware has stuck with their per socket licensing model. VMware currently only allows up to four cores per processor but with eight-core processors on the horizion, it’s probably inevitable that VMware will eventually change their licensing.