08-01 Virtualization Fundamentals Required

Virtualization is a foundational technology in modern computing that enables multiple operating systems and applications to run on a single physical machine. This lecture explores the core concepts, history, and types of virtualization.

What is Virtualization?

General Definition

Virtualization refers to creating a virtual (rather than physical) version of computing resources. In the context of this course:

• A machine implemented in software, rather than hardware
• A self-contained environment that acts like a computer
• An abstract specification for a computing device (instruction set, memory, etc.)

Common Distinction

There are two main categories of virtual machines:

1. Language-Based Virtual Machines

• Instruction set usually does not resemble any existing architecture
• Examples: Java VM, .NET CLR, Python VM
• Designed for platform independence and security

2. Virtual Machine Monitors (VMM) or Hypervisors

• Instruction set fully or partially taken from a real architecture
• Virtualizes complete hardware systems
• Examples: VMware, Xen, KVM, Hyper-V

This course focuses primarily on hypervisor-based virtualization used in cloud computing.

History of Virtualization

The evolution of virtualization technology:

1972 → IBM VM/370
       First VM architecture for mainframe machines
       
1997 → Virtual PC for Mac
       Connectix brings virtualization to personal computers
       
1999 → VMware Virtual Platform
       Commercial virtualization for x86 architecture
       
2003 → Xen Hypervisor
       Open-source hypervisor project launched
       
2005 → VMware Player
       Free VM player for end users
       
2007 → VirtualBox
       Cross-platform virtualization software
       
2010s → Cloud Era
       AWS, Azure, GCP built on virtualization

Virtualization Terminology

Understanding the key terms:

Guest OS vs Host OS

• Guest OS: The operating system running inside the virtual machine
• Host OS: The operating system running on the physical machine (for Type 2 hypervisors)
• Physical Machine (PM): The actual hardware
• Virtual Machine (VM): The virtualized environment

Type 1 Hypervisor (Bare Metal)

┌─────────────────────────────────────┐
│     Virtual Machine 1  │  VM 2      │
│  ┌──────────────┐  ┌──────────────┐ │
│  │  Guest OS 1  │  │  Guest OS 2  │ │
│  └──────────────┘  └──────────────┘ │
├─────────────────────────────────────┤
│      Type 1 Hypervisor              │
├─────────────────────────────────────┤
│      Hardware (CPU/RAM/Disk)        │
└─────────────────────────────────────┘

• Runs directly on hardware
• No need for a host operating system
• Better performance and efficiency
• Examples: VMware ESXi, Xen, Hyper-V, KVM
• Used in: Data centers, cloud providers

Type 2 Hypervisor (Hosted)

┌─────────────────────────────────────┐
│     Virtual Machine 1  │  VM 2      │
│  ┌──────────────┐  ┌──────────────┐ │
│  │  Guest OS 1  │  │  Guest OS 2  │ │
│  └──────────────┘  └──────────────┘ │
├─────────────────────────────────────┤
│      Type 2 Hypervisor              │
├─────────────────────────────────────┤
│         Host OS                     │
├─────────────────────────────────────┤
│      Hardware (CPU/RAM/Disk)        │
└─────────────────────────────────────┘

• Runs as an application on top of a host OS
• Easier to set up and use
• Slightly lower performance due to host OS overhead
• Examples: VMware Workstation, VirtualBox, Parallels Desktop
• Used in: Development, testing, desktop virtualization

Properties of Virtual Machines

Virtual machines provide four key properties that make them valuable:

1. Partitioning

• Run multiple operating systems on one physical machine
• Divide system resources between virtual machines
• Each VM gets allocated CPU, memory, disk, and network resources

Example:

Physical Server: 64 GB RAM, 16 CPU cores
├── VM1 (Web Server):    16 GB RAM, 4 cores
├── VM2 (Database):      32 GB RAM, 8 cores
└── VM3 (App Server):    16 GB RAM, 4 cores

2. Isolation

• Fault isolation: If one VM crashes, others continue running
• Security isolation: VMs are separated at the hardware level
• Performance isolation: Resource controls prevent “noisy neighbor” problems

Benefits:

• Secure multi-tenancy in cloud environments
• Contain security breaches
• Predictable performance

3. Encapsulation

• Save entire VM state to files
• Move and copy VMs as easily as files
• Snapshot and restore VM states

Use Cases:

# VM files typically include:
- .vmdk / .vdi  → Virtual disk files
- .vmx / .vbox  → VM configuration
- .nvram        → BIOS settings
- .vmem         → Memory snapshot

This enables:

• Easy backup and disaster recovery
• VM migration between hosts
• Template-based deployment

4. Hardware Independence

• Provision or migrate any VM to any physical server
• Abstract hardware from the operating system
• Standardized virtual hardware regardless of physical hardware

Advantages:

• Workload mobility across different hardware
• Simplified hardware upgrades
• Cloud provider flexibility

How Virtualization Works

The Illusion

The VM gives users an illusion of running on a physical machine:

• Applications run normally without modification
• OS believes it has direct hardware access
• Users interact with VM like a real computer

The Reality

Behind the scenes:

1. Operating systems normally run in privileged mode
   • Direct access to hardware
   • Can execute privileged instructions
2. VM OSs run in user mode
   • No direct hardware access
   • Privileged instructions are trapped
3. Most instructions execute directly
   • Hardware executes them without hypervisor intervention
   • Provides near-native performance
4. Resource management handled by hypervisor
   • Memory allocation
   • Peripheral access
   • CPU scheduling
5. Privileged instructions are “trapped”
   • Hypervisor intercepts them
   • Emulates the instruction
   • Returns control to VM

Hardware Assistance

Modern CPUs include virtualization support:

• Intel VT-x (Intel Virtualization Technology)
• AMD-V (AMD Virtualization)

These provide:

• Hardware-assisted virtualization
• Improved performance
• Better security isolation

VM Components

A virtual machine virtualizes several key components:

1. CPU Virtualization

• Virtual CPUs (vCPUs) mapped to physical CPUs
• CPU scheduling by hypervisor
• Support for multiple CPU architectures

2. Memory Virtualization

• Virtual memory presented to guest OS
• Memory management by hypervisor
• Techniques like memory ballooning and page sharing

3. Network Virtualization

• Virtual network interfaces
• Virtual switches and routers
• Network isolation and bridging

4. Disk Virtualization

• Virtual disks stored as files
• Thin provisioning and snapshots
• Multiple disk formats (VMDK, VHD, QCOW2)

Storage and Migration

• VM is stored as a file → Easy to save and migrate
• Can be moved along with apps and configuration
• Enables cloud elasticity and disaster recovery

Paravirtualization

An alternative approach to full virtualization:

Concept

• VM OS knows about virtualization
• Makes specific hypercalls instead of privileged instructions
• Requires modified guest OS

Advantages

• Better performance than full virtualization
• More efficient resource usage
• Lower overhead

Example: Xen

Xen hypervisor uses paravirtualization:

• Guest OS modified to make hypercalls
• Direct communication with hypervisor
• Used by early AWS EC2 instances

Modern Trend

• Hardware-assisted virtualization has reduced the need for paravirtualization
• Most modern systems use full virtualization with hardware support
• Paravirtualization still used for specific optimizations (e.g., virtio drivers)

Comparison: Type 1 vs Type 2

Real-World Applications

Cloud Computing

All major cloud providers use virtualization:

• AWS: Xen, KVM (Nitro), bare metal options
• Azure: Hyper-V
• Google Cloud: KVM

Enterprise Data Centers

• Server consolidation (reduce physical servers)
• Disaster recovery and business continuity
• Test and development environments

Desktop Virtualization (VDI)

• Virtual desktops for remote workers
• Centralized management
• Enhanced security

Summary

Virtualization is a cornerstone technology that:

✓ Enables multiple VMs on a single physical machine
✓ Provides isolation for security and fault tolerance
✓ Allows easy migration and backup through encapsulation
✓ Abstracts hardware for flexibility and portability
✓ Powers modern cloud computing platforms

In the next lecture, we’ll dive deeper into how virtualization works internally, including binary translation and dynamic translation techniques.