VT-d support needed in CPU...or not?

[kelu]

Hi

Can someone *please* explain why everyone says that VT-d is a chipset-ONLY feature, when all the processors at ark.intel.com have a "Intel Virtualization Technology for Directed I/O (VT-d)" tag saying either yes or no?

For example, try to select two brand new desktop Core i7 processors at ark.intel.com:
Core i7-2600
Core i7-2600K

Using the compare-feature, reveals that Core i7-2600 supports both VT-x and VT-d, while Core i7-2600K only supports VT-x....same thing with other processors. What is the point of this when tons of comments from even Intel employees claims that VT-d is a chipset-ONLY feature and not a CPU feature?

Thank in advance...
--
Kelu

[kelu]

Actually some processors have an empty field instead of yes/no:
http://ark.intel.com/Compare.aspx?ids=43556,46497,52214,52213,

A couple of recent posts from Intel employees saying that VT-d is not related to the CPU at all:
http://software.intel.com/en-us/blogs/2010/04/02/does-my-product-support-intel-vt/
http://software.intel.com/en-us/forums/showthread.php?t=78861&o=a&s=lr

[Anthony_B_Intel]

While it is true that the hardware that makes VT-d work is in the chipset, that doesn't necessarily mean the processor doesn't have to do anything toenable this feature. If VT-d is important to you, I would select CPU and chipset that both asserted support for VT-d. Not also that you need BIOS support for VT-d as well.

I don't know what to make of those entries with blank lines. I'd still look for a "yes" to be on the safe side.

[kelu]

Thank you for your answer, however, I already have three systems running with VT-d, so it's not because I'm looking for a specific system that would work, I'm looking for the reasoning behind the VT-d tag on the CPUs on ark.intel.com.

I came across another forum thread, in which the OP gets a confirmation from a "Intel Marketing Manager", who "confirms" that ark.intel.com is simply wrong, since it's just a chipset feature and not a CPU feature.

But, in the same thread there's another user who posts the follow, which in case it's true, makes a lot of sense:

VT-d is a feature of the memory controller, which now happens to be in the CPU for Nehalem and later systems. For systems prior to Nehalem, you need support in the chipset. All CPU's require a MB BIOS that supports VT-d.

For example, a Q6600 is listed as having no VT-d support, which is correct. The CPU itself does not have any VT-d functions. However, if you put that CPU into a MB with a Q35 or a Q45 chipset, VT-d works perfectly well, as long as you have a BIOS update that turns on VT-d support.

The difference is with Nehalem and later CPUs, if support is listed as "no" in ARK, you cannot add VT-d support to the system through the chipset. If "yes" appears in ark, and you put this in a MB that supports VT-d, VT-d will work just fine.

Source: http://serverfault.com/questions/142952/intel-xeon-virtualization-feature-vt-d-directed-io-chipset-feature

I have used VT-d on a workstation with a Q6600 (has an empty VT-d status on ark) a while ago, which matches the explanation above quite good.

I suppose this can be summed up as:

• VT-d support: "Empty" = Old CPU, if you can find a motherboard which fits and have VT-d support in the BIOS, it'll work fine.
• VT-d support: "No" = New CPU without VT-d support. Will never work.
• VT-d support: "Yes" = New CPU with VT-d support. Will work if the BIOS has VT-d support.

Can anyone (perhaps from Intel) confirm this?