A Virtual Machine, also known as a VM, is a software system that allows us to install Operating Systems inside other Operating System, in one computer.

The Operating System that your computer came with is called the HOST Operating System.

Operating Systems installed inside Virtual Machines are called Virtual OS. You can install multiple Virtual OS inside a Virtual Machine (VM). You can also have multiple VMs inside your HOST OS.

How regular computers work
A HOST computer contains its own OS, and its hardware such as Monitor, hard disk, mouse, keyboard, camara, etc. You can create multiple users in a HOST computer, such as you, your brother, your father, your mother, etc. The main problem with this setup is that if any user allows a virus into your computer ALL users are affected.

Benefits of Virtual computers
If you want to have multiple users in one machine you can install a Virtual Machine, and in it, you can install multiple Operating Systems, each independent of each other, all Virtual OSs use the same hardware that the HOST computer has, including the Internet access and printers accessible to the HOST.

If any of the Virtual OS gets a virus all other OSs including the HOST wil NOT be affected by the infected OS. If a Virtual OS becomes unstable you can delete it without affecting all other Virtual OSs or the HOST OS.

All Virtual OS can be cloned.
Let`s install a Virtual Windows and name it master. Do all the Windows updates and install all the basic software you need. Now use this installation as your Windows master to clone/create new Windows Virtual machines. You can do the same for any Operating System.

Installing your master copy of an OS can take hours, however once you have a Virtual Master OS created it can take less than 15 minutes to create a new installation from your master, by cloning it.

A Virtual OS is just a folder in your HOST computer, cloning simply copies the master folder to a new folder for the new Virtual OS.

You can also copy these folders (VM) to other computers and run them there.

If you need to use Linux but you have a Mac or a Windows machine, you do NOT need to buy another computer, just install a Virtual Machine and a Virtual OS in one machine. If you are using a laptop then you only carry one laptop with multiple Virtual Operating Systems.

If you need to create a network with a server and multiple nodes to test systems, you do NOT need to buy multiple computers, you can create a Virtual network in one computer, like a laptop with multiple Virtual Operating Systems.

How do we Install the VM
First find out if your HOST computer's OS is running in 32 bits or 64 bits

Download your preffered Virtual Machine. I mostly use VirtualBox for many reasons, it always works, it also allows me to run VMware Virtual OS, and it is FREE.

Install your Virtual Machine

Now using your OS disk, install it in your Virtual Machine, the VM is going to ask you how much disk space and RAM you want to give to the new Virtual OS you are installing. Every Virtual OS can have different amounts of hard disk and RAM assigned to it.

I have seen installations with 6 terabytes of hard disk storage and 128 gigabytes of RAM. In these HOST computers we can install dozens of Virtual OS/users allowing the users to connect to them from the outside via the internet or a local intranet. These installations provide great benefits to the owners and the users.

The cost of one HOST computer/server is a lot less than having dozens of separate computers. The hardware maintenance, upgrades, and backups are a lot less expensive. The amount of space is much less, the electrical and air conditioning costs are highly reduced. Adding new users or replacing a damaged Virtual OS is much faster and less expensive. For the users being able to access their Virtual OS from anywhere at anytime is priceless.

I believe that this route our industry is taking will increase productivity at all levels and reduce costs greatly.

This is a simplyfied view of what Data Centers do, and we know as "The Cloud"

The current largest provider of Cloud services is Amazon, one of its clients is Netflex. There are other providers like Microsoft Azure, Apple, ...