Virtual machines (VMs) are computers that run inside of other computers using a process known as virtualization.
What is a virtual machine?
A virtual machine (VM) is a software-based computer within another computer’s operating system, often used for testing, backing up data, or running SaaS applications. To grasp how VMs work, it’s essential to understand how an operating system typically integrates computer software and hardware.
What is an operating system?
Traditional computers are built from physical hardware, including hard disk drives, processor chips, RAM, and more. To utilize this hardware, computers rely on a type of software known as an operating system (OS). Some common examples of OSes are Mac OSX, Microsoft Windows, Linux, and Android.
The OS is what manages the computer’s hardware in ways that are useful to the user. For example, if the user wants to access the Internet, the OS directs the network interface card to make the connection. If the user wants to download a file, the OS will partition space on the hard drive for that file. The OS also runs and manages other pieces of software. For example, it can run a web browser and provide the browser with enough random access memory (RAM) to operate smoothly.
Typically, operating systems exist within a physical computer at a one-to-one ratio. for each machine, a single OS manages its physical resources.
Can you have two or more operating systems on one computer?
It is possible to run multiple operating systems on one computer. This can be achieved through a process called virtualization. In virtualization, a piece of software behaves like an independent computer. This piece of software is called a virtual machine, also known as a ‘guest’ computer. (The computer on which the VM is running is called the ‘host(s). The guest has an OS as well as its virtual hardware.
‘Virtual hardware’ may sound like an oxymoron. A VM’s ‘hard drive’ is just a file on the host computers(). However, a virtual hard drive fulfills the same function as a physical one.
The number of VMs that can run on one host is limited only by the host’s available resources. The user can run the OS of a VM in a window like any other program, or they can run it in fullscreen so that it looks and feels like a genuine host OS.
What are virtual machines used for?
Everyday use cases for virtual machines on single computers include:
- Testing – Software developers often want to test their applications in different environments. They can use virtual machines to run their applications in various OSes on one computer. This is simpler and more cost-effective than testing on several different physical machines.
- Running software designed for other OSes – Although specific software applications are only available for a single platform, a VM can run software designed for a different OS. For example, a Mac user who wants to run software designed for Windows can run a Windows VM on their Mac host.
- Running outdated software – Some older software can’t be run in modern OSes. Users who want to run these applications can run an old OS on a virtual machine.
- Browser isolation – Browser isolation is the practice of ‘isolating’ web browser activity away from the rest of a computer’s operating system to keep malware from affecting the computer’s other files and programs. Some browser isolation tools use VMs to establish this isolation — though this approach can slow browsing activity.
How does cloud computing use virtual machines?
Several cloud providers offer virtual machines to their customers. These virtual machines typically live on powerful servers that can host multiple VMs and be used for various reasons that wouldn’t be practical with a locally-hosted VM. These include:
- Running SaaS applications – Software-as-a-service, or SaaS for short, is a cloud-based method of providing software to users, in which an application is served to users over the Internet rather than running on their computers. Often, it is virtual machines in the cloud that do the computation for SaaS applications as well as deliver them to users. If the cloud provider has a geographically distributed network edge, the application will run closer to the user, resulting in faster performance.
- Backing up data – Cloud-based VM services are famous for backing up data because the data can be accessed from anywhere. Cloud VMs provide better redundancy, require less maintenance, and scale better than physical data centers. (For example, buying an extra gigabyte of storage space from a cloud VM provider is relatively easy, but much more challenging to build a new local data server for that additional gigabyte of data.)
- Hosting services like email and access management – Hosting these services on cloud VMs is generally faster, more cost-effective, and helps minimize maintenance and offload security concerns.
- Browser isolation – Some browser isolation tools use cloud VMs to run web browsing activity and deliver safe content to users via a secure Internet connection
