What is a virtual machine in OS?

A virtual machine (VM) is an emulation of a computer system within a physical computer. It allows you to install and run an operating system and applications inside the VM, isolated from the rest of the systems and resources on the physical machine. Some key features of VMs in an OS environment include:

What is a virtual machine in OS?

Portability: VMs can easily be moved, copied, and reassigned between host servers to reallocate resources efficiently.

Isolation: Issues on the VM do not affect the host hardware or other VMs running on it. Likewise, host crashes do not impact the VMs.

Encapsulation: The VM runs as a file on the host, encapsulating an entire machine state including CPUs, storage, network adapters etc.

Hardware independence: A VM is not tied to the underlying physical hardware, allowing it to run on any compatible host.

Better utilization: You can run multiple VMs optimizing hardware utilization on a single powerful host server.

Sandboxing: VMs provide an isolated and controlled environment for applications, testing software, and analytics.

How does a virtual machine work?

A VM emulates a complete hardware environment to allow a guest OS and software to function just like a physical computer. It works by inserting a thin software abstraction layer called the “hypervisor” between the hardware and the virtual machine.

The hypervisor partitions the physical resources to simultaneously run multiple VMs in isolation. It directly interacts with the hardware and intelligently distributes resources like CPU time, RAM, storage and network bandwidth to give each VM the illusion that it is running on dedicated compute hardware.

The guest OS and applications inside the VM are not aware that they are sharing resources with other VMs. Each one functions fully independently with its own virtualized CPU, memory, storage, network adapters etc. provided by the hypervisor. The end user can interact with each VM as a separate physical computer.

Types of virtualization

There are two main types of virtualization used in an OS environment:

Hardware virtualization

In hardware virtualization, the hypervisor runs directly on the server hardware to control resource access between VMs. This provides near native performance but may require specific virtualization support in the hardware like Intel VT-x or AMD-V instruction sets. Examples of hardware virtualization products include VMware ESXi and Microsoft Hyper-V.

OS level virtualization

In OS level virtualization, the base operating system runs natively on the hardware while the hypervisor runs on top as an application. This may impact performance marginally but allows virtualization on standard hardware. Examples include Docker on Linux, Jails in FreeBSD and Windows Subsystem for Linux (WSL).

Benefits of virtual machines

Some major benefits provided by virtual machines include:

Cost efficiency

Consolidating applications and workloads onto fewer powerful host servers reduces hardware and operating costs substantially.

Better utilization

Resources can be allocated as needed to match workload demands, eliminating wasteful overprovisioning. The utilization rates using virtualization can exceed 80% compared to as low as 10-15% on non-virtualized servers.

Energy efficiency

Having fewer active physical servers draws less power and reduces air conditioning demands in the data center. Studies estimate around 80% lower energy costs using server virtualization.

Improved availability

Hypervisors enable advanced high availability (HA) features like live VM migration and rapid restarts in case of underlying host failures, significantly improving uptime.

Agile operations

Provisioning a VM using templated images takes just minutes compared to hours or days to procure and configure new hardware servers. This allows faster responses to new demands.

Improved security

The strong separation between VMs on a single server greatly restricts malware spread or security breaches compared to containers or physical servers.

Challenges with virtual machines

Some key virtualization challenges that still persist include:

  • Performance overheads: Additional hypervisor abstraction can cause 5-15% overhead for CPU and memory intensive applications. This is improving rapidly with hardware assist and paravirtualization features.
  • Storage/IO bottlenecks: Storage and IO throughput are shared between multiple VMs and workloads. Performance critical systems still need direct attached hardware access.
  • Migration complexity: Although VMs can be easily migrated, coordinating stateful application and data migrations introduces significant complexity.
  • Security: While strong VM isolation limits security risks, the hypervisor itself is a prime target for attacks. Strict configuration hardening is essential.
  • Licensing costs: Many proprietary operating systems and software still have complex virtualization licensing policies that can get expensive.

The future of virtualization

As hardware assisted virtualization matures and becomes ubiquitous across computing platforms ranging from mobile to the cloud, some emerging usage trends include:

  • On-demand cloud VMs allowing near instantaneous provisioning of IT resources
  • Microsegmentation architectures isolating workloads using thousands of lightweight VMs
  • Edge computing integrating VMs into IoT devices and sensors at the network edge
  • Container-optimized OS platforms combining the portability of containers with security of VMs

So while virtual machines have already become integral to modern computing, continued innovation around security, management and integration with other technologies should further grow their adoption and capabilities.

Conclusion

In closing, virtual machine is a broad technology concept that applies to emulating hardware environments in software. VMs allow guest operating systems to access virtualized processor cores, memory, storage and devices.

The hypervisor creates isolated compartments on a host server and intelligently manages how these virtual machines access the underlying physical resources.

VMs bring cost, utilization, automation and security advantages compared to running workloads directly on dedicated hardware servers. The abstraction does incur some performance overheads but the capabilities have made virtualization integral to computing from smartphones to the cloud. Continued innovation around nested virtualization, security and management will further grow its capabilities and adoption.

Frequently Asked Questions

  1. What is a VM in simple terms?
    A VM is a software program that emulates a full computer system including devices, operating systems and applications. It runs on top of a physical server and shares resources with other VMs isolated from each other.

  2. What does a VM consist of?
    A VM consists of a set of specification files containing configuration and state information + virtual disk files that represent the guest storage devices. Together these emulate a computer’s hardware including CPU, memory, storage and network adapters that allow installing OSes and software.

  3. What is a hypervisor?
    The hypervisor is a software layer that creates and manages the virtual machines on a host server. It allocates resources from the physical hardware to guest VMs and isolates them from each other. Examples include VMware vSphere, Microsoft Hyper-V and Oracle VM VirtualBox.

  4. How is a VM different from Docker?
    Docker provides application containerization using shared operating systems whereas VMs allow encapsulating entire guest operating systems. Containers have high portability and performance but lower isolation and hardware emulation capabilities compared to VMs.

  5. Can you run software inside a VM?
    Yes, a VM emulates real hardware so you can install any compatible operating system on it e.g. Windows 10, Linux distributions or FreeBSD. This then allows installing and running software applications inside the guest OS or using it for application development.

  6. Is a virtual machine slower?
    CPU and memory intensive applications can have around 5-15% performance overhead on VMs due to the hypervisor abstraction and context switches between guest OSes. However for many workloads, this difference is negligible while the benefits like automation and sandboxing outweigh the overheads.

  7. Are VMs secure?
    VMs provide very strong isolation between workloads using separate guest operating systems. This restricts any malware or security issues on one VM from spreading outside even on the same physical server, which is a major security benefit.

  8. Can you convert a physical machine to a VM?
    Physical to virtual (P2V) conversions are commonly done using VMware vCenter Converter or Microsoft Virtual Machine Converter solutions. These copy over the disks/partitions from a source physical computer to virtual disk files usable in VMware, Hyper-V, VirtualBox etc.

  9. How does network connectivity work with VMs?
    Virtual networking components like virtual switches manage connectivity between VMs, the host hardware and external networks by mapping virtual network cards in VMs to physical network adapters on the server. This allows normal TCP/IP networking from within guest OSes.

  10. Do VMs improve performance?
    Running multiple VMs on fast virtualization capable hardware improves utilization from around 15% on non-virtualized servers to over 80% by sharing resources efficiently between workloads. However single-threaded performance is still faster on physical hardware without virtualization overheads.

  11. Can you run Windows on macOS using VMs?
    Yes, VMware Fusion and Oracle VM VirtualBox are popular hypervisors for Mac that allow creating Windows 10 and other x86 OS VMs on both Intel and Apple silicon Mac hardware. X86 binaries are emulated efficiently or you can run ARM specific Windows 11 builds natively.

  12. Do gaming PCs support VMs?
    Retail gaming motherboards and CPUs generally support hardware visualization features required for intensive VMs usage scenarios like gaming, 3D/CAD and video production workloads. Nvidia and AMD also offer hypervisor drivers and GPU pass-through technologies on select GPUs to improve graphics performance for VMs.

  13. What are examples of OS virtualization?
    At the operating system level virtualization examples include Docker containers on Linux, Jails in FreeBSD, Windows Subsystem for Linux (WSL) and Application Guard on Windows. These isolate user-space instances sharing the base host OS kernel instead of fully emulating separate guest OSes.

  14. What is virtualization in cloud computing?
    Cloud computing platforms like AWS EC2, Azure Virtual Machines and Google Compute Engine provide on-demand VMs using rapid provisioning of preconfigured VM images. These offer convenient scalability and metered pricing models without companies needing to setup their own virtualization infrastructure.

  15. What is virtualization in Android?
    The Android operating system itself runs on the Linux kernel while keeping apps and their data in isolated namespaces known as Virtual Machines. Conceptually similar isolation mechanisms operate the Dalvik or Android Runtime environments in which compiled Java apps from multiple developers securely run.

  16. What is the difference between hypervisor and virtual machine?
    The hypervisor creates, manages and monitors the full life cycle of virtual machines on a host using physical resources allocated to them. A virtual machine is an isolated guest environment with emulated CPUs, storage and devices consuming resources allocated by the hypervisor.

  17. Why do we use VMware?
    VMware vSphere and other products are highly popular in enterprise IT for bringing consistent environments for operating systems and apps across on-premise and cloud infrastructure. Benefits driving adoption include workload mobility, business continuity, optimized infrastructure costs and accelerated software delivery.

  18. What are the performance requirements for running VMs?
    Server hardware is normally recommended, but basic VMs with just CPU emulation and RAM allocation can run even on lower spec desktops. For larger or more resource intensive VMs – fast multi-core CPUs, adequate RAM to split between guest OSes, SSD/NVMe storage, dedicated NICs and GPU pass-through significantly boost performance.

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