Overview
A vCPU (virtual Central Processing Unit) is a logical unit of compute capacity, not a physical object. It represents a time-share on a physical CPU core, managed by a hypervisor.
If a physical processor core is a worker, a vCPU is an assigned task slot for that worker.
vCPU in general virtualization
In virtualization (VMware, VirtualBox, cloud platforms), the system maps virtual resources to physical hardware. Physical CPUs with Simultaneous Multithreading (SMT) — Hyper-Threading on Intel — can often run two execution threads per core.
vCPU in AWS
AWS uses vCPUs as the standard unit for EC2 instance capacity and account limits.
- Intel/AMD instances: one physical core typically equals two vCPUs (SMT enabled).
- AWS Graviton (ARM): no SMT — one vCPU equals one physical core.
- Account limits: total vCPU quota caps how many instances you can run across types.
Example: m5.xlarge
- Specification: 4 vCPUs
- Physical mapping: 2 physical cores
- Math: 2 cores × 2 threads/core = 4 vCPUs