A virtual machine (VM) is a software-defined computer that runs a full guest OS inside a host system, using virtual CPU, RAM, disk, and NICs managed by a hypervisor; each VM is isolated so failures don’t spread. VMs matter because they let many “computers” share one box, boosting efficiency, flexibility, compatibility, and security powering data centers, DevOps, testing, and legacy support. Type-1 (bare-metal) hypervisors (ESXi, Hyper-V Server, Xen, KVM) run on hardware for performance and isolation; Type-2 (Workstation, VirtualBox, Parallels, QEMU user space) run atop a host OS and suit desktops and labs. Compared to containers, VMs include their own kernel (heavier, stronger isolation, mixed-OS); containers share the host kernel (lighter, faster); many teams run containers on VMs. Key components: vCPU scheduling, mapped memory (ballooning/overcommit), virtual disks (VMDK/VHDX/QCOW2, snapshots), and vNICs via virtual switches/NAT/bridge.
Benefits include isolation, consolidation, rapid cloning/snapshots/migration, legacy compatibility, and DR via image replication. Common uses: dev/test, server consolidation, legacy apps, malware sandboxes, education. Performance is near-native for CPU; optimize I/O with paravirtual drivers (VirtIO/VMXNET3), SR-IOV, NVMe, NUMA tuning. Manage resources with careful CPU overcommit, memory ballooning/TPS, right-sized RAM; choose thin vs thick storage; segment networks (VLAN/VXLAN) with policies. Resilience: HA restarts, live migration, fault tolerance, DR/CDP. Security: patch hosts, minimize devices, use Secure Boot/TPM, segment traffic, least privilege, clean templates.
Plan for licensing and ops costs; monitor CPU Ready, IOPS/latency, ballooning/swapping, network errors. Best practices: start small and scale, use paravirtual drivers, align storage, automate (Terraform/Ansible), maintain golden images.Troubleshoot CPU contention, memory pressure, storage latency, and network MTU/VLAN issues. Deploy on-prem, cloud, or hybrid; choose VMs when you need OS diversity, stronger isolation/compliance, system-level drivers, or legacy/GUI workloads; modernize over time and consider P2V/V2V. Capacity and governance: baseline, keep 20–30% headroom, separate latency-sensitive apps, tag/CMDB, encrypt, back up and drill, audit changes. Quick start: pick a hypervisor, set shared storage and networks, build templates, establish backup/monitoring/patching, and document lifecycle. In short: VMs deliver robust isolation and control; containers deliver speed and density; most real-world stacks blend both.
