I just have a quick question regarding EC2. Its to do with CPU sharing on Amazon EC2. Amazon supports a number of different instance types, be it small, medium, large etc. Each of these has a number of virtual cores assigned to them. My question is this, if the physical host has for instance 8 cores and I instantiate an m1.small instance which has 1 virtual cpu, what happens when I request CPU cycles? Are the CPU cycles being taken off multiple physical cores (i.e. across all 8 if any are idle) or is there a dedicated single physical core that is assigned to my VM.



The former option - from any available free core - that's the default for any hypervisor although most will allow you to 'peg' a VM to a specific core if there's a good reason for doing so.

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