Virtualization allows multiple virtual machines (VMs) to run on a single physical machine. To achieve this, virtualization can be implemented at different levels in a computer system. These levels define how virtualization is done and what components are affected.
1. Instruction Set Architecture (ISA) Level
- At this level, virtualization is done by emulating one ISA on another.
- Example: Running MIPS code on x86 hardware.
- Uses code interpretation or dynamic binary translation.
- Useful for running legacy applications on modern hardware.
- Slow performance, but high flexibility.
2. Hardware Level
- Virtualization happens directly on the hardware.
- Uses a software layer called Hypervisor (or Virtual Machine Monitor).
- Example: Xen hypervisor, IBM VM/370.
- Allows running multiple OSes on the same hardware.
- Gives high performance and good hardware utilization.
3. Operating System (OS) Level
- Virtualization is done above the OS kernel.
- Creates containers or OS instances.
- Example: Docker, LXC containers.
- Efficient and used for server consolidation and cloud hosting.
- All containers must use the same OS kernel.
4. Library Support Level
- Virtualization is done at the API/library level.
- Controls how applications communicate with system libraries.
- Example: WINE runs Windows apps on Linux.
- Example: vCUDA allows GPU usage in VMs.
- Simple to implement, but has limited flexibility.
5. User-Application Level
- Virtualizes individual applications as processes.
- Also called process-level virtualization.
- Example: Java Virtual Machine (JVM), .NET CLR.
- Another form: Application Sandboxing (e.g., LANDesk).
- Good for application isolation and easy distribution.
Comparison of Different Levels:
