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optional · CSS study notes

Virtual Machines

CSS Optional — Paper-II, Computer Organization & Architecture

1. Definition

A virtual machine (VM) is a software abstraction that emulates a complete computer system, allowing software built for one platform to run in an isolated environment on different underlying hardware.

2. Classification — By Scope

  • Process VM — runs a single program inside a managed runtime.
    • Example: Java Virtual Machine (JVM).
  • System VM — emulates an entire OS environment on top of physical hardware.
    • Example: a VMware or VirtualBox guest OS.

3. Classification — Hypervisor Types

  • Type 1 (bare-metal) — runs directly on hardware; no host OS underneath.
    • Examples: VMware ESXi, Xen, Microsoft Hyper-V.
    • Used in: data centers, enterprise cloud infrastructure.
  • Type 2 (hosted) — runs as an application on top of a host OS.
    • Examples: VirtualBox, VMware Workstation.
    • Used in: desktop testing, development sandboxes.

🗺️ Architecture Diagram — Hypervisor Types

graph TD
    subgraph T1["Type 1 - Bare Metal"]
        H1["Hardware"] --> HV1["Hypervisor"] --> VM1A["Guest VM"]
        HV1 --> VM1B["Guest VM"]
    end
    subgraph T2["Type 2 - Hosted"]
        H2["Hardware"] --> OS2["Host OS"] --> HV2["Hypervisor"] --> VM2A["Guest VM"]
        HV2 --> VM2B["Guest VM"]
    end

4. Benefits of Virtualization

  • Isolation — a fault in one VM does not affect others.
  • Portability — the same VM image runs on any compatible host.
  • Server consolidation — multiple VMs run on one physical server, improving hardware utilisation.
  • Security sandboxing — untrusted code runs contained within a VM.

🎯 CSS Exam Angle

Increasingly relevant given cloud-computing questions appearing more often in recent CS-optional papers.

🔁 Repeated CSS Questions

  1. What is a virtual machine? Differentiate between Type 1 and Type 2 hypervisors.
  2. How do virtual machines enable cloud computing and server consolidation?
  3. Compare virtualization with containerization. (Increasingly asked as a follow-up)

⚠️ MCQ Trap

Type 1 hypervisor = bare-metal (no host OS underneath, used in enterprise/cloud); Type 2 = hosted (needs an underlying OS, used for desktop testing) — examiners frequently swap these in MCQs.