Intel VT-x is an instruction set that facilitates virtualization. From Wikipedia
The CPU flag for VT-x capability is "vmx" […]
"vmx" stands for Virtual Machine Extensions, which adds ten new
instructions: VMPTRLD, VMPTRST, VMCLEAR, VMREAD, VMWRITE, VMCALL,
VMLAUNCH, VMRESUME, VMXOFF, and VMXON.
But
With some motherboards, users must enable Intel's VT-x feature in the
BIOS setup before applications can make use of it
With some motherboards, VT-x technology is disabled by default and you have to go into the BIOS settings to enable it, while with other instruction sets, like SSE, that is not the case.
What would be the disadvantages of enabling this instruction set by default?
Best Answer
This is how I would think as a manufacturer and what I would do:
Considerations:
Effect: VT-x is a gateway to the entirely "new world" in the computer, because it gives a way to functionality of cardinality of original PC. This opens equally big space for potential issues.
How many users will actually use that? 2-10% of people who purchase the motherboard? Others are typically happy if their computer is working for basic use.
What advantages will default enablement bring to ordinary users? None. Until they discover it, learn it and start using it. Unlike other board features, it won't boost system performance, improve connectivity or sound or anything else immediately visible.
Are there risks of default enablement for ordinary users? Yes. Security - virtual machines potentially installed as malware and running without users knowing. Or at least performance and stability. E.g. CPU usage is reported differently. We do not need basic users to blame us for anything (and call our support) while actually it's them who do not understand what they are doing.
▶ Enable it by default? Based on the above, no. Make the enablement optional for users who are interested in it.
I think main reasons are rather non-technical than technical.