What are Virtual Machines: Best Virtual Machine Explained 2021

What are Virtual Machines

There are many reasons why your company might consider using virtual machines. VMs allow for reduced overhead, with multiple systems operating from the same console at the same time. VMs also provide a safety net for your data, as they can be used to enable rapid disaster recovery and automatic backups.

Intro to Virtual Machines

A virtual machine, commonly shortened to just VM, is no different than any other physical computer like a laptop, smart phone, or server. It has a CPU, memory, disks to store your files, and can connect to the internet if needed. While the parts that make up your computer (called hardware) are physical and tangible, VMs are often thought of as virtual computers or software-defined computers within physical servers, existing only as code.

A virtual machine is a computer that does not physically exist as a piece of hardware. The hardware that is seen by the operating system is emulated in an effort to separate the physical hardware from the operating system. This allows the virtual machine to be moved and hosted on any machine independent of hardware.

How do Virtual Machines work?

Virtualization is the process of creating a software-based, or “virtual” version of a computer, with dedicated amounts of CPU, memory, and storage that are “borrowed” from a physical host computer such as your personal computer and/or a remote server such as a server in a cloud provider’s datacenter.

Why virtualization is required in os: A virtual machine is a computer file, typically called an image, that behaves like an actual computer. It can run in a window as a separate computing environment, often to run a different operating system or even to function as the user’s entire computer experience as is common on many people’s work computers. The virtual machine is partitioned from the rest of the system, meaning that the software inside a VM can’t interfere with the host computer’s primary operating system.

What are VMs used for?

Here are a few ways virtual machines are used:

  • Building and deploying apps to the cloud.
  • Trying out a new operating system (OS), including beta releases.
  • Spinning up a new environment to make it simpler and quicker for developers to run dev-test scenarios.
  • Backing up your existing OS.
  • Accessing virus-infected data or running an old application by installing an older OS.
  • Running software or apps on operating systems that they weren’t originally intended for.

What are the benefits of using VMs?

While virtual machines run like individual computers with individual operating systems and applications, they have the advantage of remaining completely independent of one another and the physical host machine. A piece of software called a hypervisor, or virtual machine manager, lets you run different operating systems on different virtual machines at the same time. This makes it possible to run Linux VMs, for example, on a Windows OS, or to run an earlier version of Windows on more current Windows OS.

And, because VMs are independent of each other, they’re also extremely portable. You can move a VM on a hypervisor to another hypervisor on a completely different machine almost instantaneously.

Because of their flexibility and portability, virtual machines provide many benefits, such as:

Cost savings

Running multiple virtual environments from one piece of infrastructure means that you can drastically reduce your physical infrastructure footprint. This boosts your bottom line—decreasing the need to maintain nearly as many servers and saving on maintenance costs and electricity.

Agility and speed

Spinning up a VM is relatively easy and quick and is much simpler than provisioning an entire new environment for your developers. Virtualization makes the process of running dev-test scenarios a lot quicker.

Lowered downtime

VMs are so portable and easy to move from one hypervisor to another on a different machine—this means that they are a great solution for backup, in the event the host goes down unexpectedly.


VMs allow you to more easily scale your apps by adding more physical or virtual servers to distribute the workload across multiple VMs. As a result you can increase the availability and performance of your apps.

Security benefits

Because virtual machines run in multiple operating systems, using a guest operating system on a VM allows you to run apps of questionable security and protects your host operating system. VMs also allow for better security forensics, and are often used to safely study computer viruses, isolating the viruses to avoid risking their host computer.

The pros of Virtual Machines

Less physical hardware. In a typical distributed control system (DCS), you might have two Tag/OS servers, two batch servers, a historian or two, and an engineering station or two. Easily, you’re looking at six servers that will need to be physically maintained. You’ll find a time and overall cost savings on the replacement of hardware and maintenance.

Central location to manage all assets.

All of your virtual machines can be managed from one location.

More eco-friendly.

If you look at your current configuration, most of your machines are idling along. But, with them virtualized and running on a cluster, you maximize your machines’ potential while saving money on energy costs.

Disaster recovery is quick.

Re-deploy virtual machines on your system (once you get the host machine back online) and you can have your system back up and running in no time.

Expansion potentials.

With the infrastructure in place, it’s simply a matter of deploying a new machine and configuring. No need to go buy new servers (assuming you didn’t cheap out and buy bottom-of-the-line servers).

System upgrades.

The time and heartache of making system images before applying a patch and having a system restore fail are all realities. With the virtual environment, if something goes wrong while applying a patch or update, you can simply roll back the virtual machine back where it was before you applied the patch using a snapshot.

Software licensing.

Many software packages (such as Rockwell products) tie a license key to a hard drive ID. In a virtual environment, the hard drive ID stays the same no matter which piece of hardware it is running on.

Supports legacy operating systems.

As hardware evolves and operating systems become obsolete, it’s harder to find hardware and software that are compatible. Virtualizing these machines eliminates the operating system compatibility problems. This doesn’t fix the problem of obsolete operating systems that are no longer supported-which is a security risk.

Forward compatibility.

As new hardware becomes available, your virtual machines can still run on this new hardware (as long as it is supported by the virtual host software).

Use of thin clients.

Using a thin client manager, replacement of a bad terminal is as easy as a few clicks and powering on the new unit. Conversely, with a physical machine you’re stuck with re-imaging or building a replacement from scratch.

Many of the pros are related to the VMware ESXi/Sphere platform. The company has done a great job of packing high-availability features into its product:

  • Monitors if a virtual machine has stopped running and restarts automatically (App High Availability).
  • Can move a virtual machine running on one server to another without shutting down the guest virtual machine (VMotion).
  • Can move a virtual machine running on one SAN to another without shutting down the guest machine (Storage VMotion).
  • Automatically powers on a guest machine on boot of the server.

The cons of virtual machines


The upfront cost can be much higher and, depending on how high of an availability you want, you’ll need to be willing to design the system for your needs now and in the future.


If you’re not familiar with the hardware and network aspects of the whole setup, it can be daunting to figure out. Routing rules and virtual local area networks (VLAN) continue to add complexity, especially if security is a concern.

Often the hardware is bundled together in one location,

Making a single disaster more likely to cause significant downtime. However, there are ways around this.

Hardware keys.

Yes, you can use hardware keys. You can bind a USB port to a specific virtual machine. However, you are not able to move the virtual machine without physically moving the key as well.

Add-on hardware.

In the past, you weren’t able to add on older PCI hardware and share it with the virtual machine. This has changed, but it doesn’t work 100% of the time. I’d recommend testing it thoroughly before deploying. Of course, this also limits which machine a virtual machine can run on because it will need to be bound to that piece of hardware.

What to consider befor using VM

Server, switch, and SAN power.

You’re going to want to have servers with dual power supplies. Each of these power supplies will need a separate circuit to run on. We typically separate them to a UPS circuit and a regular line circuit each powered from different panels.


Usually, on a control system we recommend having a closed system (not connected to the corporate IT or Internet in the plant). I’ve not covered security in this article, as that is another topic entirely.

Virtualization options.

There are other platforms than VMWare to virtualize with; Microsoft has its own system, which is powerful, along with many other virtual hosting options. I’ve not evaluated how other systems compare against VMware, so we’ll leave that as a topic for another day.

Connections to virtual machines.

Connections to virtual machines can be established through remote desktop connections. Many thin clients have the ability to connect directly to a virtual machine that is running; this provides the look and feel of having a physical machine. Thin clients work much like a KVM routing the keyboard, mouse, video, and audio from the user to the virtual machine.

Virtual machine maintenance.

Some maintenance can be performed on a virtual machine. My Colleague Chris Hardy has written a blog on maintenance that focuses on VMWare’s workstation version 16 can be downloded, but the concepts still apply for maintenance.

Virtual Machines FAQ

Why do developers use virtual machines?

Virtual Machines lend themselves well to testing different configurations and setups. Developers can use VM snapshots to try various scenarios, and then quickly and easily restore the environment. This allows developers and software testers to identify configuration problems before end users run into them.

What can I do with a virtual machine?

– Disaster Recovery Has Never Been Easier.
– Saving Data From a Legacy System.
– Testing a New Operating System or Software.
– Hang Onto Old Apps.
– A True Internet Sandbox.

What is the main function of virtual machine?

Overview. A virtual machine (VM) is a virtual environment that functions as a virtual computer system with its own CPU, memory, network interface, and storage, created on a physical hardware system (located off- or on-premises).

What is a virtual machine and why is it useful?

At its base level, a virtual machine (VM) is software that runs programs or applications without being tied to a physical machine. In a VM instance, one or more guest machines can run on a physical host computer.

Can virtual machines get viruses?

When there is an antivirus or antispyware program installed in the virtual machine then there is less of a chance that the virtual machine will become infected by a virus. Just as on physical computers, the programs will continue to scan and attempt to remove threats if any are found.

What is the main disadvantage of virtual memory?

Applications may run slower if the system is using virtual memory. Likely takes more time to switch between applications. Offers lesser hard drive space for your use. It reduces system stability.

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