CPUs/vCPUs vs Memory

When choosing a virtual machine, the most relevant ratio to consider is the ratio of CPU cores to memory (RAM). Or, if a virtual machine has simultaneous multithreading/Hyper-Threading enabled, consider the ratio of vCPUs (virtual CPUs) to memory.

Multithreading/Hyper-Threading enables multiple threads to run concurrently on a single CPU core. Each thread is represented as a virtual CPU (vCPU) on the instance. Therefore, if a virtual machine has two CPU cores and two threads per core, it has four vCPUs in total.

For more information see https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/cpu-options-supported-instances-values.html.