Q. I notice the A0 on the Azure page now shows 1 CPU instead of .25. Does it no longer share a core?
A. The number of CPUs shown for VMs shows the number of vCPUs that are present in the VM rather than the actual physical cores. Azure uses many different generations of hardware with different processor capabilities but its critical for users that no matter which generation of hardware their VMs are deployed to a consistent performance is assured. Azure limits how much of a CPU core can be used by vCPUs to assure performance consistency and since this would vary across generations trying to show a percentage of a real core would not be logical.
Azures uses the Azure Compute Unit (ACU) to show the CPU measure for each vCPU the various VM sizes which is documented at https://docs.microsoft.com/en-us/azure/virtual-machines/virtual-machines-windows-sizes?toc=%2fazure%2fvirtual-machines%2fwindows%2ftoc.json. This document currently shows the A0 with an ACU of 50 per core which is half than the 100 of the A1 to A7.