By Sailee Shingare | M.S. in Computer Science, Northern Illinois University (NIU)
In my last post, I said the cloud is essentially “someone else’s computer.” But how does one physical computer serve thousands of customers at the same time?
The answer is virtualization.
The Problem Virtualization Solves
Imagine you have a powerful server sitting in a data center. It has 64 CPUs and 256GB of RAM.
You only need 4 CPUs and 16GB of RAM for your application. The rest sits idle — wasted, expensive hardware doing nothing.
Now imagine 16 different companies with the same problem. Each has a powerful server, each using only a fraction of it.
Virtualization solves this by letting one physical server act as many separate computers simultaneously.
What is Virtualization?
Virtualization is the process of creating a software-based version of something that is normally physical — like a computer, server, or network.
Instead of one server running one operating system, virtualization lets you run multiple virtual machines (VMs) on a single physical machine. Each VM behaves like a completely independent computer with its own:
- Operating system
- CPU allocation
- Memory
- Storage
- Network settings
From the outside, each VM looks and acts like a real physical server. Nobody can tell the difference.
How Does it Work?
The magic happens through a piece of software called a Hypervisor.
A hypervisor sits between the physical hardware and the virtual machines. It manages and allocates resources — deciding how much CPU, memory, and storage each VM gets.
There are two types:
Type 1 Hypervisor (Bare Metal) Runs directly on the physical hardware. No underlying operating system needed. Faster and more efficient. Examples: VMware ESXi, Microsoft Hyper-V, Xen
Type 2 Hypervisor (Hosted) Runs on top of an existing operating system. Easier to set up, great for personal use. Examples: VirtualBox, VMware Workstation
Think of the hypervisor as a traffic controller — directing resources to each VM based on demand.
A Simple Analogy
Think of a large apartment building.
Become a Medium member
The physical server is the building. The hypervisor is the building manager. Each virtual machine is a separate apartment — self-contained, private, with its own address and utilities.
The tenants (applications) in each apartment have no idea they’re sharing the same building. To them, they have an entire home to themselves.
Why Virtualization Matters for the Cloud
Cloud providers like AWS, Azure, and GCP use virtualization at massive scale.
When you launch an EC2 instance on AWS, you’re not getting a dedicated physical server. You’re getting a virtual machine running on a physical server shared with other AWS customers — completely isolated from each other.
This is how AWS can offer thousands of virtual servers on demand within seconds. They’re not buying new hardware every time — they’re carving up existing hardware into virtual slices.
Virtualization enables:
- Faster provisioning — spin up a new server in seconds
- Better resource utilization — no wasted hardware
- Isolation — each VM is completely separate from others
- Snapshots and backups — save the entire state of a VM instantly
- Portability — move VMs between physical servers easily
Virtualization vs The Cloud
These terms are often confused. Here’s the difference:
Virtualization is the technology — the ability to create virtual machines from physical hardware.
The Cloud is the service built on top of virtualization — where someone else manages that virtualized infrastructure and you access it over the internet.
You can have virtualization without the cloud (running VMs in your own data center). But you can’t have the cloud without virtualization.
Try it Yourself
Want to see virtualization in action for free?
- Download VirtualBox at virtualbox.org — it’s free
- Download an Ubuntu ISO at ubuntu.com/download
- Create a new VM in VirtualBox using the Ubuntu ISO
- Boot it up
You just ran a completely separate Linux computer inside your Windows or Mac machine. That’s virtualization.
What’s Next?
Now that you understand virtualization, you’re ready for the next step — containers.
Containers took the ideas of virtualization and made them even lighter, faster, and more portable. They’re the foundation of modern cloud-native applications — and the reason Docker and Kubernetes exist.
We’ll cover that in the next post.
