Virtualization and Cloud Computing
What to know
Virtualization lets one physical host run many isolated guests. A Type 1 hypervisor runs directly on hardware (VMware ESXi, Microsoft Hyper-V Server, Proxmox) and is used in data centers; a Type 2 hypervisor runs as an application on a desktop OS (VirtualBox, VMware Workstation, Parallels). Guests need the host CPU’s virtualization extensions (Intel VT-x / AMD-V) enabled in UEFI - a classic “VM won’t start” answer. Allocate RAM and storage carefully, since overcommitting causes swapping and poor performance. Snapshots capture a point-in-time state and are not backups; a long snapshot chain grows and slows the VM. Containers share the host OS kernel, start fast, and are lighter than VMs but offer less isolation. VDI hosts desktop images centrally and streams them to thin clients.
Cloud service models: IaaS provides raw compute, storage, and networking (EC2, Azure VMs); PaaS provides a managed runtime for developers (App Service, Heroku); SaaS provides finished applications (Microsoft 365, Gmail, Salesforce). Deployment models are public, private, hybrid, and community. Key characteristics: on-demand self-service, broad network access, resource pooling, rapid elasticity, and measured service (pay-as-you-go). Under the shared responsibility model, the provider secures the physical infrastructure and the customer secures data, identities, and access.
Traps. Do not confuse Type 1 and Type 2 numbering; “bare metal” signals Type 1. A snapshot is not a backup. SaaS is chosen when the user only needs the application, not the platform.
Rule of thumb. Ask who manages what: if the customer manages only data and users, it is SaaS; if they manage the OS, it is IaaS.
Worked example. A firm moves email to a hosted service and manages no servers: SaaS.