CompTIA A+ Core 1 (220-1101) — Study Guide for the retired V14 exam

Introduction

Virtualization and cloud computing let organizations run workloads flexibly instead of buying a physical server for every job. This is the smallest domain on Core 1, but it is conceptual rather than fact-dense, so it rewards clear understanding over memorization. This chapter explains the hypervisor and the two types of it, the difference between containers and virtual machines, the three cloud service models, and the deployment models and shared characteristics that shape planning.

The through-line is abstraction and sharing: virtualization abstracts one physical machine into many logical ones, and cloud computing sells that capacity as a metered, on-demand service. Each concept is a step up the ladder of "how much does someone else manage for you."

Virtualization basics

Virtualization abstracts physical hardware so multiple operating systems can run on one machine. The hypervisor is the software layer that makes this possible.

• The hypervisor manages VMs. It abstracts the hardware and allocates CPU, memory, and storage to each virtual machine. Firmware, drivers, and bootloaders are low-level components but they do not manage VMs — the hypervisor does.
• Type 1 runs on bare metal. A Type 1 (bare-metal) hypervisor installs directly on the hardware, with no host OS beneath it, for maximum performance — the enterprise data-center pattern.
• Type 2 runs on a host OS. A Type 2 (hosted) hypervisor runs as an application on top of an existing operating system — the way you run a test VM on a laptop.
• Isolation aids testing. VMs isolate environments, so a lab or a piece of development work does not affect the host — a safe sandbox.

Type 1 vs. Type 2 — the trade-off. A bare-metal (Type 1) hypervisor gives better performance and stronger isolation because nothing sits between it and the hardware; it is what data centers use. A hosted (Type 2) hypervisor is more convenient — you install it like any app on a working desktop — at the cost of the overhead of the underlying OS. Convenience versus performance is the whole distinction.

Containers vs. virtual machines

Containers are a lighter alternative to full VMs: they isolate applications while sharing the host's kernel instead of each carrying a whole operating system.

• Containers share the host kernel. They package an app with its dependencies so it runs consistently across environments, without bundling a full OS.
• VMs include a full guest OS. Each VM carries its own operating system, which makes it heavier than a container.
• Containers start fast and scale well. Their light footprint suits microservices and rapid deployment.
• Choose based on isolation needs. Full VMs give stronger isolation; containers give density and speed. That is the design decision.

Cloud service models

Cloud providers deliver computing at different levels of abstraction, from raw infrastructure up to finished applications. The higher you go, the more the provider manages for you.

• IaaS — Infrastructure as a Service. You get virtual compute, storage, and networking and manage them yourself. Most control, most responsibility.
• PaaS — Platform as a Service. You deploy applications onto a managed platform without managing the underlying OS and servers. The provider handles the plumbing; you handle the app.
• SaaS — Software as a Service. You use a fully managed application — webmail, an online office suite — through a browser. Least to manage, least control.
• Responsibility shifts by model. Moving from IaaS → PaaS → SaaS hands more of the management burden to the provider and leaves you less to run.

Cloud deployment and characteristics

Beyond what is delivered, clouds differ in who owns them, and they share defining traits that guide planning.

• Public clouds are multi-tenant. A provider hosts shared infrastructure used by many customers.
• Private clouds are dedicated. Infrastructure serves a single organization for control and compliance.
• Hybrid combines both. A hybrid cloud links on-premises and public resources so workloads can move between them. (A community cloud, by contrast, is shared among several related organizations — not the same as hybrid.)
• Elasticity and measured service. Elasticity means resources scale up or down automatically with demand; measured service means usage is metered so customers pay for what they consume (pay-as-you-go).

Resource planning. Before creating multiple VMs on a host — or sizing a cloud deployment — the resource that matters is the host's available CPU cores, RAM, and storage, and for an individual VM the administrator tunes its allocated vCPUs and RAM in the hypervisor. Over-committing beyond what the host can supply is what turns a tidy virtualization plan into a slow one.

Key facts & specs

Every item in this box is drawn from this book's source material for the virtualization and cloud domain.

Worked example — matching the model to the need

"We want fully managed email our staff just log into in a browser." That is a finished application — SaaS. "Our developers want to push code to a managed platform without patching servers." Platform, no OS management — PaaS. "We need virtual machines and virtual networks we control and configure ourselves." Raw infrastructure — IaaS. "Keep sensitive workloads in our own data center but burst to a public provider at peak." On-prem plus public, workloads moving between them — a hybrid deployment. The tell is always how much you want to manage yourself (IaaS most, SaaS least) and who owns the infrastructure (private, public, or hybrid).

Common traps

• Swapping Type 1 and Type 2. Type 1 = bare-metal (on hardware, enterprise); Type 2 = hosted (on top of an OS).
• Thinking a container includes a full OS. It does not — it shares the host kernel. The VM carries the full guest OS.
• Mixing up the service models. IaaS = infrastructure, PaaS = platform, SaaS = software. Webmail is the classic SaaS example.
• Confusing hybrid with community. Hybrid = private + public together; community = shared among related organizations.
• Forgetting the host's limits. VMs draw on the host's real CPU, RAM, and storage — plan capacity before spinning them up.

Self-check

1. Which hypervisor type installs directly on the hardware with no host OS? (Type 1, bare-metal.)
2. How does a container differ from a virtual machine? (A container shares the host kernel and is lightweight; a VM carries a full guest OS and is heavier.)
3. Which cloud service model delivers finished applications like webmail? (SaaS.)
4. What does "measured service" mean? (Usage is metered so customers pay only for what they consume.)
5. Which deployment links on-premises and public cloud so workloads can move between them? (Hybrid.)