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As I understand it, I should be allowed 8 virtual processors per core, and 4 per VM.

How do I find out why I'm being limited to two, and how to overcome that?

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How do you know you are being limited? Do the extra cores not show in the options? – Mark Henderson Oct 24 '12 at 20:16
@MarkHenderson Correct. In the 'number of logical processors' dropdown, I can only select "1" or "2" – Wesley Oct 24 '12 at 20:18
I think the more important question is why you want to overcome that, and map more cores to a VM than you have physically. There are easier ways to make your system unbearably slow, after all, and in most cases, adding extra cores to a VM only makes performance worse, rather than better. – HopelessN00b Oct 24 '12 at 20:37
@HopelessN00b I only need one VM. We need to sandbox a transition to SharePoint 2013 RTM, which requires 4 cores and my install is failing with two. Machine doesn't need to be fast, just an environment for a dry run. – Wesley Oct 24 '12 at 21:09
up vote 6 down vote accepted

The Intel Xeon X5150 is a dual-core CPU that was used in systems from mid-2006 until 2007.

It ran in systems that could accommodate two CPU sockets, so at most, you can have four usable cores if both sockets are populated. If only one CPU socket is populated, you won't be able to create a virtual machine with more than two cores.

In a VMWare, Hyper-V or similar virtualization scenario, that means that you won't be able to take advantage of the higher advertised CPU core limits.

I'm guessing your system only has one physical CPU.

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You also wouldn't want to. While some hypervisors like ESXi can assign more logical cores to a VM than the host has, the extra emulation introduced makes things crawl. – Falcon Momot Oct 24 '12 at 20:25
From what I understand, though, this is inaccurate. Reference:… "Each core very safely support 8 virtual processors. Logical processors are abstractions of time of the physical processors and really muddy the thinking as they apply to a physical machine one way and to a hypervisor in a different way." – Wesley Oct 24 '12 at 20:25
@Wesley That article is a bit misleading. You can't overprovision a single host like that, nor would you want to. You can overprovision a group of VMs on a server. For example, in your 4 physical core situation, you can easily have 8 VMs with 1 core each. You cannot, however, have 1 VM with 8 cores. – MDMarra Oct 24 '12 at 20:47
Gotcha. So my VM that needs a minimum of 4 cores to run SP2013 will need to be on another machine. Thanks! – Wesley Oct 24 '12 at 21:08

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