A Virtual Machine (VM) is a software-based computer that runs an operating system and applications just like a physical computer.
It behaves like a real machine but uses virtualized hardware resources provided by a physical host.
👉 A Virtual Machine is a “computer inside a computer.”
It has:
But physically, all these resources come from one host machine.
Every VM contains:
| Term | Meaning |
| Host | Physical machine |
| Guest | Virtual machine |
| Hypervisor | Software managing VMs |
Host provides:
The guest runs independently.
1️⃣ Hypervisor installed on the host
2️⃣ VMs created with allocated resources
3️⃣ Guest OS installed
4️⃣ VM runs like an independent system
Even though VM shares hardware, it works as a separate system.
Imagine a powerful server with:
You create:
| VM | OS | Purpose |
| VM1 | Windows Server | Web server |
| VM2 | Linux | Database |
| VM3 | Ubuntu | Testing |
| VM4 | Windows | File server |
All run on same physical server.
Each VM:
If one VM crashes → Others continue running.
Cloud providers offer VMs as:
You rent VM instead of buying hardware.
🔹 Snapshot
Save current state of VM.
🔹 Clone
Copy existing VM.
🔹 Live Migration
Move VM from one host to another without downtime.
🔹 Resource Allocation
Increase RAM or CPU dynamically.
| Feature | Physical Machine | Virtual Machine |
| Hardware | Dedicated | Shared |
| Cost | High | Low |
| Scalability | Slow | Fast |
| Backup | Complex | Easy |
| Deployment | Slow | Quick |
✅ Cost effective
✅ Easy deployment
✅ Better resource utilization
✅ Isolation
✅ Testing environment support
✅ Disaster recovery
❌ Performance slightly lower than physical
❌ Requires powerful host
❌ Resource contention possible
❌ Licensing cost (sometimes)
Modern IT infrastructure:
Understanding VM is fundamental for:
“Virtualization architecture” refers to the structural design that explains how virtualization technology is implemented between hardware, hypervisor, and virtual machines.
It shows:
There are mainly 3 main layers:
1️⃣ Physical Hardware
2️⃣ Hypervisor (Virtualization Layer)
3️⃣ Virtual Machines (Guest OS)
Includes:
This is the real physical machine.
The Hypervisor is the most important part of virtualization architecture.
It:
Each VM contains:
VMs are isolated from each other.
There are two major types:
Architecture Flow:
Hardware → Hypervisor → Virtual Machines
Architecture Flow:
Hardware → Host OS → Hypervisor → Virtual Machines
| Feature | Type 1 | Type 2 |
| Installed On | Hardware | Host OS |
| Performance | High | Medium |
| Use Case | Enterprise | Personal/Lab |
| Security | More secure | Less secure |
Hypervisor manages:
It ensures fair resource distribution.
If hypervisor compromised → All VMs affected.
Cloud data centers use:
This allows:
Think of:
The manager allocates rooms & resources to each apartment.
If the interviewer asks:
You can say confidently:
“A virtual machine is a software-based computer that runs an operating system and applications using virtualized hardware resources from a physical host machine. It allows multiple operating systems to run on a single physical server efficiently.”
Virtual Machines (VMs) have four fundamental properties that make virtualization powerful and reliable:
1️⃣ Partitioning
2️⃣ Isolation
3️⃣ Encapsulation
4️⃣ Hardware Independence
These properties define how virtualization works in modern IT infrastructure.
📖 Definition
Partitioning means dividing the physical hardware resources (CPU, RAM, Storage, Network) into multiple logical units so that multiple VMs can run simultaneously on one physical host.
👉 One big server divided into smaller virtual computers.
Each VM gets assigned specific resources.
Host Machine:
Hypervisor creates:
| VM | vCPU | vRAM |
| VM1 | 4 | 16GB |
| VM2 | 4 | 16GB |
| VM3 | 4 | 16GB |
| VM4 | 4 | 16GB |
Each VM runs independently but shares same physical hardware.
✅ Better hardware utilization
✅ Multiple workloads on one server
✅ Flexible resource allocation
✅ Scalability
Isolation ensures that each VM operates independently and does not interfere with other VMs on the same host.
👉 Problem in one VM does not affect others.
If one VM crashes → others continue running.
Malware inside one VM does not spread automatically to other VMs.
Each VM gets allocated CPU and RAM limits.
If:
Because hypervisor isolates resources.
Encapsulation means that a virtual machine is stored as a set of files on the host system.
The entire VM (OS, applications, settings) is contained inside files.
👉 A VM is just a folder with files.
✅ Easy backup (copy VM files)
✅ Easy cloning
✅ Easy migration
✅ Snapshot support
You can:
No need to reinstall OS.
Hardware Independence means that VMs are not tied to specific physical hardware.
They can run on different physical machines without modification.
👉 VM does not care which physical server it runs on.
Hypervisor creates virtual hardware layer:
Even if physical hardware differs.
VM running on:
Can be migrated to:
Without reinstalling OS.
✅ Live migration
✅ Disaster recovery
✅ Cloud scalability
✅ Easy hardware upgrades
| Property | Meaning | Benefit |
| Partitioning | Dividing hardware resources | Better utilization |
| Isolation | Separate environments | Security & stability |
| Encapsulation | VM stored as files | Easy backup & migration |
| Hardware Independence | Not tied to hardware | Flexibility |
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