HyperVisors and Virtual Machines

1. Virtual Machine Monitor / Manager (Hypervisor)

Definition: A layer of software/firmware managing multiple VMs on a single physical host.

• Types of Hypervisors:

  • Type 1 (Bare Metal): Runs directly on hardware. Examples: VMware ESXi, Microsoft Hyper-V Server, Xen.
  • Type 2 (Hosted): Runs on an existing OS. Examples: VMware Workstation, Oracle VirtualBox, Parallels Desktop.

• Key Functions:

  • Virtualization
  • Resource Allocation
  • Isolation
  • Hardware Abstraction

• Advantages:

  • Server Consolidation
  • Isolation
  • Ease of Management

• Use Cases:

  • Data Centres
  • Development and Testing
  • Desktop Virtualization

• Challenges:

  • Performance Overhead
  • Security Concerns
  • Compatibility

• Key Providers: VMware, Microsoft, Citrix, Oracle

2. Implementation Types

• Type 1 Hypervisor:

  • Direct control over hardware.
  • Efficient performance.
  • Used in enterprise environments.

• Type 2 Hypervisor:

  • Runs on top of a host OS.
  • Easier setup.
  • Used for desktops/laptops.

3. Para-Virtualization

• Implementation: Modifies the guest OS for efficient communication with the host.
• Example: Xen (uses Xen-aware Linux kernel).
• Characteristics: Improved performance but requires guest OS modifications.

4. Programming Environment Virtualization

• Approaches:
  • Virtual Machines: Full-fledged emulation of a computer system. Examples: VMware, VirtualBox, Hyper-V.
  • Cloud-based Environments: IDEs or services in the cloud. Examples: AWS Cloud9, GitHub Codespaces.
• Advantages: Isolation, compatibility, accessibility, collaboration.

5. Emulation

• Definition: One system behaves like another.
• Examples: Dolphin, Parallels, Wine, Bluestacks, Xcode.
• Advantages: Cross-platform compatibility, low cost, space efficiency.
• Disadvantages: Slower performance, security risks.

6. Microkernels and Exokernels

• Microkernels:

  • Principle: Minimize kernel functionality, delegate services to user-space.
  • Structure: Core services in the microkernel, additional services in user-space.
  • Advantages: Modularity, reliability.
  • Disadvantages: Performance overhead, complexity.
  • Examples: Mach, L4.

• Exokernels:
  

  • Principle: Expose hardware resources directly to applications.
  • Structure: Minimal abstractions, direct hardware management by applications.
  • Advantages: Performance, flexibility.
  • Disadvantages: Security concerns, complexity for developers.
  • Examples: Exokernel, Nemesis.

• Comparison:

  • Abstraction Level: Microkernels (higher-level), Exokernels (lower-level).
  • Performance: Microkernels (potential overhead), Exokernels (maximum performance).
  • Flexibility: Microkernels (modularity), Exokernels (direct control).
  • Security: Microkernels (isolation), Exokernels (application-level responsibility).

Summary

Microkernels focus on modularity and reliability, with a small core kernel, while exokernels prioritize performance and flexibility by allowing applications direct hardware control. The choice depends on design goals and trade-offs. Hypervisors, essential for virtualization, come in two types: Type 1 for direct hardware access and Type 2 for ease of use on existing OS. Emulation and programming environment virtualization facilitate cross-platform compatibility and consistent development setups.