Intel
Intel CPUs require EM64T and VT support in the chip and in the BIOS.
Note: If VT is enabled on an ESX host, the vmx flag is found in /proc/cpuinfo.
Intel EM64T CPUs do not have segmentation support in long mode. If the Intel EM64T CPU is VT-capable, it comes with hardware virtualization support (Intel's Virtualization Technology). This hardware virtualization support allows VMware to work around the lack of segmentation, making it possible to run 64-bit guest operating systems on Intel EM64T VT-capable CPUs.
Notes:
Firmware/BIOS support is required to enable Intel Virtualization Technology. Some systems (particularly laptops) do not have the necessary firmware/BIOS support to enable Intel Virtualization Technology, and cannot run 64-bit guest operating systems.
In multi-processor systems, all processors must support compatible VT implementations. At a minimum, all processors must implement the same VMCS revision ID. In multi-processor systems with mixed processor steppings, 64-bit guest operating systems may not be supported.
Many servers that include CPUs with VT support might ship with VT disabled by default, and VT must be enabled manually. If your CPUs support VT but you do not see this option in the BIOS, contact your system vendor to request a BIOS version that lets you enable