motherboard - which is the best CPU?

I am going to buy a new CPU. I have Intel Core 2 duo 4300. I've already chosen Intel i5-2500/i5-2500k (Sandy Bridge) as my new target CPU. I've read a lot of details about Sandy Bridge family, P67/H67 chipsets. My question is about TXT/VT-d.

As Intel COMPARISON pages shows there is a (major/minor?) difference between these two CPUs: lack of TXT/VT-d in i5-2500K model.

My question is.. when exactly and in what software do these options matter? Please, share some (or many) examples of real application of these two technologies.

In theory VT-d could provide much better support for emulation and handling of hardware devices within a VM and, for example, take some of the grunt work out of moving data from the VM network interface to the host network interface.

In all honesty for home users you're probably not going to see a massive boost to your VM performance with VT-d, it looks to me more geared around multiple heavily used concurrent VMs, but there may be a bit more performance if your VM host software supports it.

See:

Understanding VT-d: Intel Virtualization Technology for Directed I/O

Intel® Virtualization Technology for Directed I/O

Intel® Virtualization Technology (Intel® VT) for Directed I/O (Intel® VT-d) Architecture Specification

Looking at that last document (section 2.5 if you're interested) VT-d's main features appear to be allowing more separation of I/O to devices from VMs (so that each VM can effectively have it's own buffer to a device) and allowing VMs with appropriate drivers to have nearly direct access to the host hardware while still remaining protected and secure.

I don't know much about TXT, but VT-d is great! Like mentioned above it allows hardware devices to be assigned directly to a virtual machine. From the VM's point of view, it is like the hardware is directly plugged in.

My use case for wanting this technology was to setup a virtualized multi-seat computer. I wanted to setup multiple VM's each as their own separate workstation, and I wanted them to have the speed and power of non-emulated 3D graphics. I.e. two or more separate gaming VM's running from the same physical box! With each VM having it's own monitor, graphics card, keyboard and mouse.

I've got two seats currently setup on my machine. Please be aware that it is non-trivial to setup and maintain. You also have to be careful with the make and model of your CPU, Motherboard and the BIOS you choose for the setup, as they all have to support VT-d for it to work. I've got it to work with the following hardware and software.

Hardware:

• Intel i5-2500 (non-k)
• AsRock Extreme 4 Gen 3 Z68 Motherboard
• ATI HD 6850
• ATI HD 6450
• 16gb ram
• 1tb storage
• 3 x Monitor/Keyboard/Mouse (the extra monitor plugs in to dom0)

Software:

• Dom0 - Debian 6, custom 3.1 kernel and Xen 4.1.2
• 1st DomU - Win 7 Home Premium
• 2nd DomU - Win 8

My setup isn't exactly the same as this guys, but check out the clip for a demonstration of what I'm talking about: http://www.youtube.com/watch?v=Gtmwnx-k2qg

There are two different aspects:

• vt-d is a useful technology allowing VMs direct access to the hardware. Beyond the obvious performance gain the other advantage is that the VM does not have to rely on the hypervisor or host OS support of the HW.

• TXT however is a potentially nastier kind of beast. Although it is presented by Intel as a security improvement for the user it is above all a device allowing vendor lock-in and DRM enforcement. And you and I know that you can't trust vendors to use these device in the sole customer's interest. I'm not saying we should boycott these CPUs, they will eventually be ubiquitous, however if you are in the process of selecting a CPU, that's probably one thing you might want to be aware of.