Difference between Azure VM core and vCPU

Question

_{Monday, January 8, 2018 1:48 AM}

From this link I cannot seem to find a term "core", but "vCPU" but I see "core" in Pricing Calculator https://azure.microsoft.com/en-us/pricing/calculator/?service=virtual-machines which gets me fairly confused at difference. Does this mean with "core" tagged to VM, I can build a nested virtualization? As far as I know nested virtualization is supported only in Dv3 and Ev3. However, from the list in Pricing Calculator page, not only Dv3 or Ev3, the term "core" is represent in F, H series and even the first D series.

Thuan Soldier

Personal Blog | Twitter | Microsoft Azure Defense In Depth Guide

All replies (4)

_{Monday, January 8, 2018 9:39 AM ✅Answered}

The naming is not related to nested virtualisation, it is related to the fact that the CPU provided to your VM has moved from being 1 to 1 with a physical core, to being a virtual CPU that is created by the Hypervisor and is  utilising Hyperthreading under the hood, and so may not be physical at all. This should be a benefit to your selection strategy, as it allows you to see which machines use physical cores and which use virtual, given that there can be performance difference between these it is an important thing to know.

Sam Cogan Microsoft Azure MVP
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_{Monday, January 8, 2018 5:51 AM | 1 vote}

You are correct that nested virtualization is supported in Dv3 and Ev3 virtual machine sizes.

Core is inside physical processor, you can have more than one operations unit, called Core. We can say that a core is like a processor, so 1 Processor with two Cores is like 2 processors with 1 Core (I insist is like not equal). Today all processors are multi-core, and for servers, we usually find 4 or more cores processors whereas Virtual CPU is a program can be allocated a number of “virtual” cores (CPUs) for execution, the operating system can choose which physical core to use (as needed).

Do click on "Mark as Answer" on the post that helps you, this can be beneficial to other community members.

_{Monday, January 8, 2018 9:24 AM}

When Microsoft moved to the Dv3/Ev3 SKU they changed from using physical cores to virtual CPU's and utlize hyperthreading on the underlying host, hence the change in the naming you see. This will continue with new machines that use virtual cores.

With the Dv3/Ev3 machines you can now use nested virtualisation. You should however also be aware of the change to Hyperthreaded CPU's, as this may result in changes in performance.

Sam Cogan Microsoft Azure MVP
Blog | Twitter

_{Monday, January 8, 2018 9:27 AM}

For nested virtualization, the discrepancy would make sense. But for non-nested virtualization VM, having core and vCPU on virtual machines lead to confusion of VM selection strategy.

Thank you for your info.

Thuan Soldier

Personal Blog | Twitter | Microsoft Azure Defense In Depth Guide