The Enhanced vmxnet adapter was already available in ESX 3.5 (see KB1001805). The support for this adapter is a lot better since Update 4 is released. Now you can also add the Enhanced vmxnet adapter to a Windows Server 2003 VM, without the workaround mentioned in KB1007195.
Some info about the Enhanced vmxnet from KB1001805:
Enhanced vmxnet — The enhanced vmxnet adapter is based on the vmxnet adapter but provides some high-performance features commonly used on modern networks, such as jumbo frames. This virtual network adapter is the current state-of-the-art device in virtual network adapter performance, but it is available only for some guest operating systems on ESX Server 3.5. This network adapter will become available for additional guest operating systems in the future.
Enhanced VMXNET is supported only for a limited set of guest operating systems:
- 32/64-bit versions of Microsoft Windows 2003 (Enterprise and Datacenter Editions). You can use enhanced vmxnet adapters with other versions of the Microsoft Windows 2003 operating system, but a workaround is required to enable the option in the VI Client. See http://kb.vmware.com/kb/1007195. Since Update 4, you can add the Enhanced vmxnet via the VIC.
- 32/64-bit versions Red Hat Enterprise Linux 5.0
- 32/64-bit versions SUSE Linux Enterprise Server 10
- 64-bit versions Red Hat Enterprise Linux 4.0
And a warning:
Migrating virtual machines that use enhanced vmxnet. Enhanced vmxnet is new with ESX Server 3.5. Virtual machines configured to have enhanced vmxnet adapters cannot migrate to older ESX Server hosts, even though virtual machines can usually migrate freely between ESX Server 3.0 and ESX Server 3.0.1.
If you must migrate a virtual machine between newer and older hosts,don’t choose enhanced vmxnet but instead one of the older adapter types. Flexible or e1000 are offered whenever enhanced vmxnet is offered.