What are the two types of virtual machines?

Virtual machines (VMs) simulate a complete computer system in software. They provide functionality, application support, and an operating system allowing programs to run as if executed on a physical computer. There are two main types of virtual machines:

What are the two types of virtual machines?

System Virtual Machines

System VMs provide a substitute for a real machine. They behave exactly like a physical computer with bios, boot sequence, devices, etc. System VMs run on bare metal with no host OS or require only a thin host OS layer.

Some examples of system VMs include:

  • VMware ESXi
  • Microsoft Hyper-V
  • Citrix XenServer

Key features:

  • Emulate physical hardware and boot sequence
  • Requires no host OS or minimal host OS layer
  • Higher performance than process VMs
  • Can run different guest OSs independently

Process Virtual Machines

Process VMs do not emulate hardware and instead simulate a program. They run as an application inside a host OS sharing underlying resources. The host OS schedules CPU/memory between the VM and other processes.

Some examples of process VMs:

  • Oracle VirtualBox
  • VMware Workstation Player
  • Parallels Desktop

Key features:

  • Runs as a process in host OS
  • Lower performance due to resource sharing
  • Supports fewer guest OS options
  • Simpler to use than system VMs

In summary, system VMs simulate an entire computer while process VMs simulate an application. System VMs offer higher performance and support more OSs but require more complex configuration. Process VMs trade performance for simplicity.

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Comparing System and Process Virtual Machines

When deciding between system and process VMs, there are several key differences to consider:

Host OS Dependencies

  • System VMs – Do not require a host OS (bare metal hypervisors) or only require a minimal host OS layer.
  • Process VMs – Require a full host OS and run within that environment as an application.

Performance

  • System VMs – Access hardware resources directly for faster performance.
  • Process VMs – Experience degraded performance due to resource sharing with host OS.

Supported Guest OSs

  • System VMs – Can run many guest OS types (Windows, Linux, etc.) independently.
  • Process VMs – Offer limited guest OS support depending on host environment.

Ease of Use

  • System VMs – Complex setup and configuration.
  • Process VMs – Very simple to install and use.

Scalability

  • System VMs – Used for large scale server, cloud, and enterprise virtualization.
  • Process VMs – Limited scalability. Mainly used on desktop systems.

Choose system VMs when maximum performance, compatibility, and scalability are required. Select process VMs for simplicity and convenience especially for desktop applications.

Common Uses of System Virtual Machines

Due to their hardware virtualization capabilities, system VMs power many enterprise-grade solutions:

Server Consolidation

  • Reduce Costs – Multiple VMs can run on a single server driving up utilization rates. Less hardware is needed lowering costs.
  • Flexible Allocation – Resources can be dynamically allocated to match VM needs. Add/remove VMs quickly.
  • High Uptime – Easily migrate VMs to other servers for failover and maintenance.

Infrastructure Optimization

  • Hybrid Cloud – Extend on-premises infrastructure to the cloud seamlessly during peak loads.
  • Storage Virtualization – Combine disparate storage devices into unified pools and dynamically allocate based on VM requirements.
  • Network Virtualization – Improve security and reliability through virtual networking and software-based layer 2/3 abstractions.

Desktop Virtualization (VDI)

  • Simplified Management – Centralize control of desktop images and configurations.
  • Enhanced Security – Protect sensitive data in the data center. VMs act as simple clients.
  • High Availability – Easily implement redundancy and fault tolerance mechanisms.

Hyperconverged Infrastructure (HCI)

  • Scalability – Scale compute and storage resources linearly through a cluster of identical nodes.
  • Resilience – Built-in data protection with software-defined RAID, replication, erasure coding, and backups.
  • Economics – Software-defined infrastructure reduces need for proprietary hardware lowering costs.

Common Uses of Process Virtual Machines

Process VMs are commonly used in development environments and for running old operating systems:

Sandbox Testing

  • Safely Test Code – Test software in contained VMs with no impact to the host environment. Revert to snapshots to quickly reset state.
  • Develop Cross-Platform – Emulate different target environments like mobile OSs during development/testing phases.

Running Legacy Software

  • Access Old Apps – Legacy and obsolete applications require outdated operating systems. Process VMs provide a compatible platform to run these apps.
  • Preserve Compatibility – Emulate the software’s original runtime environment instead of porting to new infrastructure.

Data Recovery

  • Investigate Failures – Mount drive images from corrupted systems to extract data and determine root cause of crashes.
  • Teach Security – Students can study attack methods and strengthening countermeasures in an isolated environment.

While less performant than system VMs, process VMs provide convenient sandboxing for many use cases. Their simple deployment model encourages experimentation and innovation.

Key Takeaway

There are two fundamental types of virtual machines:

  • System VMs: Simulate an entire computer system at the hardware level. Used primarily for server consolidation, infrastructure optimization, VDI, and HCI solutions.
  • Process VMs: Behave as an application to provide an isolated environment. Best suited for use cases like testing, legacy software, and data recovery that value simplicity over performance.

Selecting the right VM model involves tradeoffs between capability/compatibility and speed vs ease-of-use. Properly leveraging virtualization unlocks flexibility and efficiency in IT operations and development workflows alike.

Conclusion

Virtual machines are a pivotal technology enabling major advancements in computing over the past decades. By abstracting hardware, VMs provide portability and containment generating a wide range of technical and business benefits. Understanding the core differences between system vs process VMs allows matching the appropriate model to use case requirements around performance, compatibility, resiliency, and simplicity. Mastering virtual infrastructure unlocks immense potential for innovation.

Frequently Asked Questions

What is a System Virtual Machine?
A system VM simulates an entire computer system. It behaves like physical hardware and provides functionality, support for various operating systems, and a complete runtime environment. System VMs enable server consolidation, infrastructure optimization, VDI, and HCI solutions.

How does a System VM differ from a Process VM?
A system VM emulates a full machine with higher performance while a process VM simply behaves as an application with limited capabilities. System VMs require no host OS vs process VMs needing a complete host OS to run as an application.

What are some examples of System Virtual Machines?
Common system VM hypervisors include VMware ESXi, Microsoft Hyper-V, Citrix XenServer, Red Hat Enterprise Virtualization (RHEV), and Nutanix AHV.

What are some examples of Process Virtual Machines?
Some well-known process VMs are Oracle VirtualBox, VMware Workstation/Player, Parallels Desktop, QEMU, and WineHQ.

When should System VMs be used vs Process VMs?
Choose system VMs when hardware virtualization, flexibility, performance and compatibility are required like enterprise IT environments. Select process VMs when simplicity and convenience are priorities like developer desktops or running legacy software.

Can a host OS run without System Virtualization support?
Most modern CPUs provide hardware acceleration to run system VMs efficiently. Older CPUs lacking virtualization support can still run slower software-emulated system VMs. All CPUs support process VMs since they run as regular applications.

How are system VMs used for server consolidation?
System VMs allow servers to achieve higher utilization by running multiple workloads in isolation. Resources are flexibly allocated across VMs as needed. Consolidating servers cuts overall hardware requirements.

How do system VMs enable infrastructure optimization?
Abstractions for networking, storage and other infrastructure provided by the hypervisor simplify management, enhance resilience, and unlock flexibility to scale or reconfigure components independently.

What are the benefits of VDI using system VMs?
VDI solutions can centrally control, backup, update and secure desktop VMs running user sessions. Resources scale on-demand, and continuity features keep users productive through outages or disasters.

How do system VMs scale in Hyperconverged Infrastructure?
HCI clusters scale storage and compute linearly while the software stack automates load balancing. The architecture eliminates complex SANs enabling a building block approach to grow infrastructure seamlessly.

Why use process VMs for sandbox testing?
The isolated environment protects the underlying host from instability or corruption during testing. Snapshots easily reset state for repeated runs. Simulating target platforms speeds cross-platform development.

When should legacy software run on a process VM?
If newer infrastructure breaks compatibility with older apps, process VMs can emulate the original runtime OS and environment so software continues functioning.

How do process VMs assist data recovery?
Forensics tools can inspect drive images from corrupted systems running inside a process VM. Students also use them to study cyber attack and defense scenarios in safe sandbox environments.

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