The primary difference between a CPU and a vCPU (virtual CPU) lies in their physical versus virtual nature. A CPU is a physical hardware component, while a vCPU is a virtualized representation of CPU resources assigned to a virtual machine (VM). A vCPU uses hyperthreading.
Here's a breakdown:
CPU (Central Processing Unit)
- Physical Hardware: The CPU is a tangible piece of hardware within a computer, server, or other computing device.
- Processing Core: It's the primary processing unit that executes instructions and performs calculations.
- Direct Access: Operating systems and applications typically have direct access to the CPU's processing power.
vCPU (Virtual CPU)
- Virtual Representation: A vCPU is not a physical processor. Instead, it represents a portion of the underlying physical CPU's resources allocated to a virtual machine. As the reference states: A virtual CPU (vCPU) is a physical central processing unit (CPU) that is assigned to a virtual machine (VM).
- Hypervisor Management: A hypervisor (also known as a virtual machine monitor or VMM) manages the allocation of CPU resources to vCPUs across multiple VMs.
- Abstraction Layer: The VM interacts with the vCPU as if it were a dedicated physical CPU, but the hypervisor abstracts the underlying hardware.
Table Summarizing the Key Differences
| Feature | CPU (Physical) | vCPU (Virtual) |
|---|---|---|
| Nature | Physical Hardware | Virtual Representation |
| Tangibility | Tangible | Intangible |
| Allocation | Directly accessed | Allocated by Hypervisor |
| Hyperthreading | Not specifically related | Uses hyperthreading. |
Analogy
Think of a physical apartment building (the server with the CPUs). Each apartment (VM) needs a kitchen (CPU resources). A vCPU is like a timeshare agreement on the kitchen; multiple apartments (VMs) can use the same physical kitchen (CPU) at different times, managed by a building manager (hypervisor).
