CompTIA A+ · Operating Systems
Learn the boot methods, installation types, and partitioning decisions that govern how an operating system gets onto a machine — and what to verify before any OS change.
25 min read · OS Installations & Upgrades
// CHECK YOUR KNOWLEDGE
Installing an operating system is one of the most fundamental tasks in a technician's work. Whether you are setting up a single workstation, deploying hundreds of corporate laptops, or recovering a failing machine, you are making decisions at three levels: how the machine boots the installer, what kind of installation you perform, and how the storage is prepared. This lesson covers all three, plus what to verify before any change.
L1 established the OS landscape and filesystem types. This lesson builds on that — , , and facts here connect to L1 rather than repeat it.
Before an OS installs, the machine must boot an installer. The ( or ) reads the — a priority list of devices — and hands control to the first bootable device it finds. Where that bootable content lives is the boot method.
flash drive is the most common method today. You write an OS installer image to a USB drive, set the USB as the first boot device in BIOS/UEFI, and restart. The firmware loads the installer from the drive. USB boots are fast, portable, and work on virtually any modern machine.
Network boot () — Preboot Execution Environment, flag the expansion for verification — allows a device to boot from the network before any OS is loaded locally. When the machine powers on, the firmware contacts a server to get an address, then downloads a boot image from a deployment server on the network. The machine boots entirely over the network. PXE is the backbone of enterprise mass deployment: a technician can image dozens of machines simultaneously without touching them individually.
Solid-state/flash drives function the same as USB flash drives for boot purposes. An OS installer on an external connected via USB or another interface is bootable using the same process. Faster read speeds on SSDs can reduce install time compared to older optical or spinning-drive media.
Internet-based installation downloads the OS installer directly from the vendor's servers during the install process. Windows supports this: a minimal boot tool starts the process locally, and the full OS downloads from Microsoft during setup. This requires an active internet connection throughout the installation. Useful when you need the most current available version without pre-downloading a complete image.
External/ drive covers booting from an external drive connected via USB or . Hot-swappable means the drive can be connected and disconnected while the machine is powered on. The practical distinction from a standard USB flash drive is that this category often refers to full external hard drives or SSDs in enclosures rather than thumb-sized flash media.
Internal hard drive (partition) — a machine can boot from a different partition on the same physical internal drive. Recovery partitions work this way: the manufacturer places a hidden partition on the drive at the factory, and a key combination at boot loads that partition's recovery environment. Multiboot setups also rely on this: multiple operating systems installed on the same physical drive, each in its own partition, with a boot menu at startup. Flag for verification whether OSes in a multiboot setup must be on separate physical drives or can share one drive with separate partitions.
Multiboot deserves a note. When two or more operating systems are installed on one machine, a boot loader presents a selection menu at startup. Each OS occupies its own partition. A common configuration is dual-booting Windows alongside a Linux distribution. The boot loader — on Linux systems, the Windows Boot Manager on Windows-only machines — manages the handoff to whichever OS the user selects.
▸ NOTE
Boot order is set in BIOS/UEFI. If the machine ignores your USB installer and boots straight to the existing OS, check the boot priority in firmware settings. The installer media must be listed before the internal drive. On some systems, a one-time override menu (often F12 at startup) lets you select the boot device without permanently changing the order.
How you install the OS determines what happens to existing data and configuration on the machine.
Clean install wipes the selected partition and installs the OS from scratch. All existing data, applications, and settings on that partition are destroyed — format happens during install. The result is the cleanest possible system: no leftover software, no inherited configuration problems, no conflicts from the old installation. The mandatory prerequisite: back up all user data before starting a clean install. There is no recovery without a backup.
In-place upgrade installs the new OS version over the existing one while preserving user data, settings, and installed applications. You run the upgrade installer from within the running OS or boot it and choose "Upgrade" rather than "Custom." Windows migrates your files and settings to the new version. This is faster than a clean install and avoids reinstalling every application, but it can inherit existing problems — a misconfigured app, a corrupted entry, or a driver that does not support the new OS version will carry over.
Image deployment takes a pre-configured OS installation — called an image or — and pushes it to target machines. The image is built on a reference machine with the OS installed and configured exactly as required. Every target machine receives an identical copy. Enterprise IT uses image deployment extensively: tools include WDS (Windows Deployment Services), MDT (Microsoft Deployment Toolkit), and SCCM/MECM (System Center Configuration Manager / Microsoft Endpoint Configuration Manager). Know the concept and the tool names; you do not need to know how to configure these tools for A+.
Remote network installation installs the OS from a server over the network. The target machine boots via PXE, connects to the deployment server, and receives the installer or image remotely. The technician does not need physical access to each machine — essential for large deployments and remote branch offices.
Zero-touch deployment takes automation further: the entire installation and configuration process runs without any technician interaction at the target machine. The device is shipped to the user, the user powers it on, and the device enrolls itself, downloads its configuration, and completes setup automatically. Platforms that enable this: Windows Autopilot (Microsoft), Apple Automated Device Enrollment (), formerly known as Device Enrollment Program (DEP), delivered through Apple Business Manager, and Google Zero-Touch Enrollment — flag all three tool names for verification. Zero-touch only works when the device's serial number is pre-registered with the deployment platform before shipping.
Recovery partition is a hidden partition the manufacturer places on the drive during factory setup. Booting into the recovery partition restores the device to its out-of-box factory state — the OS and software configuration as it was when the device shipped. No external media is required. Access typically involves pressing a manufacturer-specific key combination during boot — F11 and F12 are common examples, but the exact key varies by manufacturer and model. The trade-off: a factory restore erases all user data and everything installed or configured after purchase.
Repair installation reinstalls the OS system files without removing user data, applications, or settings. Use this when Windows system files are corrupted and the machine behaves erratically, but user data must be preserved. In Windows 10 and 11, the closest equivalent is "Reset this " with the "Keep my files" option — flag this term and the exact option name for verification. This reinstalls Windows while preserving personal files, though reinstalled applications may need to be set up again.
▸ WARNING
Back up before any installation or upgrade — no exceptions. A clean install destroys all data on the partition. An in-place upgrade can fail mid-process and leave the system unbootable. A factory restore via the recovery partition erases everything since purchase. Without a backup, there is no recovery path for user data.
▸ WARNING
Recovery partition = factory reset; all user data lost. A factory restore deletes everything added after purchase: files, applications, accounts, settings. Confirm the user has a complete backup of their data before initiating a factory restore from the recovery partition.
▸ EXAM TIP
Installation type distinctions — these five are directly tested:
Before installing an OS, the storage drive must have a partition scheme applied. Two schemes exist for x86/x64 systems:
GPT is the modern standard. It is required for UEFI firmware — UEFI cannot natively boot from an MBR-formatted system drive without enabling a legacy compatibility mode (CSM) that disables UEFI security features.
Key GPT facts:
MBR is the legacy scheme, required for Legacy BIOS (also referred to as CSM mode). Key MBR facts:
▸ COMPAT
Firmware–partition scheme compatibility rule:
Modern machines pair UEFI with GPT. You will encounter MBR on older hardware or in environments that must maintain Legacy BIOS compatibility.
▸ EXAM TIP
GPT vs MBR — memorize both sets of limits:
After partitioning, the selected partition must be formatted before the OS can write to it. The Windows installer handles this automatically during a clean install: you select the target partition, the installer formats it, and then writes the OS files.
The standard filesystem for Windows system drives is NTFS — covered in detail in L1. NTFS provides the permissions, encryption, journaling, and large file support that Windows requires for its system partition. Do not choose FAT32 or for a Windows installation partition.
Format destroys all data on the partition. This is intentional during a clean install. Selecting the wrong partition and formatting it removes that data permanently.
Before changing an OS — whether clean install, in-place upgrade, or version upgrade — verify these things in order:
Back up data first. Stated in the installation types section; repeated here because it applies to every OS operation and must be the first step every time. Back up to external storage, a network share, or . Confirm the backup is complete and readable before proceeding.
Application compatibility. Not every application runs on every OS version. Check that the user's critical software — line-of-business applications, industry-specific tools, older productivity suites — is supported on the target OS. If an application requires an older Windows version, an upgrade to the newest version may break it or require a paid upgrade to the application.
Driver compatibility. Drivers are OS-specific. Before upgrading, verify that hardware — especially anything niche like proprietary scanners, older network adapters, or specialized input devices — has drivers available for the target OS version. Missing drivers after an upgrade leave hardware non-functional.
Hardware compatibility — Windows 11 requirements. Windows 11 introduced the strictest hardware requirements in Windows history. All five must be met — flag all five for verification:
▸ COMPAT
Windows 11 hardware requirements — all five must be met. A machine that satisfies four of the five fails the compatibility check. TPM 2.0 is the requirement that blocks the most older-but-otherwise-capable hardware. The Windows PC Health Check tool evaluates all five simultaneously and reports which requirements are not met.
▸ EXAM TIP
Windows 11 minimum requirements — memorize all five:
A common exam scenario: a machine fails the Windows 11 compatibility check despite having adequate CPU, RAM, and storage. The missing requirement is almost always TPM 2.0.
Windows 10 delivered feature updates twice per year (spring and fall releases). Windows 11 has shifted to an annual cadence with one major feature update per year. Feature updates are more than security patches: each adds new functionality, changes UI elements, and can affect compatibility with third-party software. Feature updates increment the Windows build version number (for example, Windows 10 22H2 or Windows 11 23H2).
Each Windows version has a defined end-of-support date. When a build version reaches that date, it stops receiving security patches. Keeping machines on supported build versions requires applying feature updates within their support window — covered in the lifecycle context established in L1.
The check questions below test your ability to choose the correct installation type, select the right partition scheme for the hardware and drive size, and apply the Windows 11 hardware requirements to real technician scenarios.
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