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Virtual Machines

What are Virtual Machines?​

A virtual machine (VM) is a software-based emulation of a physical computer that runs an operating system and applications. It creates a virtualized environment that behaves like a separate computer system, complete with virtual hardware components.

Architecture of Virtual Machines​

Components​

  1. Host Machine

    • Physical computer hardware
    • Host operating system
    • Hypervisor (VM Manager)

  2. Virtual Hardware

    • Virtual CPU
    • Virtual RAM
    • Virtual Storage
    • Virtual Network Interface

  3. Guest System

    • Operating System
    • Applications
    • Libraries
    • Dependencies

How Virtual Machines Work​

1. Hardware Virtualization​

  • Creates virtual version of:
    • Processors
    • Memory
    • Storage
    • Network interfaces
  • Each VM gets its own set of virtual hardware

2. Resource Allocation​

  • Dedicated portion of:
    • CPU cores
    • RAM
    • Storage space
    • Network bandwidth

3. Isolation​

  • Complete separation between:
    • Different VMs
    • VMs and host system
    • Applications in different VMs

Types of Virtual Machines​

1. System Virtual Machines​

  • Complete platform for running operating system
  • Full hardware virtualization
  • Examples: VirtualBox, VMware

2. Process Virtual Machines​

  • Run single program/process
  • Platform-independent execution
  • Example: Java Virtual Machine (JVM)

Advantages of Virtual Machines​

1. Complete Isolation​

  • Full separation between environments
  • Enhanced security
  • No interference between applications

2. Full OS Functionality​

  • Run any operating system
  • Access to all OS features
  • Native OS experience

3. Established Technology​

  • Mature tooling
  • Well-understood security model
  • Extensive management tools

Disadvantages of Virtual Machines​

1. Resource Overhead​

  • Each VM needs:
    • Full operating system
    • Dedicated resources
    • Virtual hardware emulation

2. Performance Impact​

  • Hypervisor overhead
  • Resource sharing inefficiencies
  • Slower startup times

3. Storage Requirements​

  • Large disk space needed
  • Multiple OS copies
  • Application duplications

VM vs. Containers: Key Differences​

1. Resource Usage​

  • VMs: Full OS + Virtual Hardware
  • Containers: Share OS kernel

2. Startup Time​

  • VMs: Minutes
  • Containers: Seconds

3. Size​

  • VMs: GBs
  • Containers: MBs

4. Isolation Level​

  • VMs: Complete hardware-level isolation
  • Containers: Process-level isolation

Use Cases for Virtual Machines​

1. Legacy Applications​

  • Running old software
  • Supporting legacy OS
  • Maintaining compatibility

2. Development and Testing​

  • Cross-platform testing
  • OS-specific development
  • Isolated testing environments

3. Server Consolidation​

  • Multiple servers on one machine
  • Resource optimization
  • Cost reduction

4. Disaster Recovery​

  • System backups
  • Quick recovery
  • Environment replication

Best Practices​

1. Resource Management​

  • Proper sizing of VMs
  • Resource monitoring
  • Performance optimization

2. Security​

  • Regular updates
  • Network isolation
  • Access controls

3. Backup Strategy​

  • Regular snapshots
  • Data backup
  • Recovery testing

Next Steps​

Understanding virtual machines helps appreciate why containers were developed and their advantages. In the next sections, we'll explore:

  1. Docker components
  2. Container architecture
  3. Practical usage of containers