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How to perform a Windows 11 ISO file install
The days of IT departments manually provisioning Windows OSes and company settings onto each PC are long gone, but IT staff still should know how to deploy OSes via ISO file.
IT administrators can install Windows OS instances with several different methods. But sometimes the approach of a Windows ISO file is preferrable because it delivers a clean OS without requiring any physical contact.
Organizations and their IT staff should learn how Windows ISO files work, what methods there are to install them and how to pick the best Windows install approach.
How Microsoft distributes Windows OSes
Microsoft used to distribute Windows on various forms of physical media starting with floppy disks. When Windows 95 made its debut, it appeared on CD-ROM. That practice continued until Windows XP's release in 2001 appeared on DVDs. DVDs persisted until Microsoft switched over to ISO formats and online distribution in 2007 for Windows 7 and future OSes.
Today, Microsoft offers download pages for Windows 10 and 11, and administrators can use these downloads to create their own ISOs.
Figure 1 shows the contents of a current Windows 11 ISO file downloaded in mid-2024. It's mounted as the E drive, with contents mapped out in the freeware program, WizTree. There are two especially large files that are part of the package:
- Install.wim. This is the Windows image file used to install the complete Windows OS.
- Boot.wim. A Windows image file used to boot a PC into the Windows Preinstallation Environment (WinPE) when performing a clean install, or to run repair or recovery tools on an existing install.
There are other Microsoft sources for Windows ISOs:
- The Visual Studio subscriptions download page. A paid account is required.
- The Windows Insider Preview Downloads page. This is for pre-release versions of Windows 10 and 11 and a verified account is required.
- Reputable third-party Windows ISO sources, including UUP dump, which custom builds ISOs on demand, accessing only Microsoft servers. HeiDoc.net also offers a Microsoft Windows and Office ISO Download Tool, mostly for older Windows and Office versions with Microsoft's permission.
How to use an ISO file to install Windows
There are two basic ways to apply a Windows ISO file to a desktop: a repair install or an install by booting from media that includes the ISO's contents.
How to perform a Windows ISO repair install
The repair approach requires the target PC to run Windows. That means it will work only in circumstances where the OS is still working well enough to run File Explorer and execute programs, specifically the Windows installer named Setup.exe.
Right click the ISO file name in Explorer. Then, select Mount from the pop-up menu, as shown in Figure 2. This mounts the ISO as a virtual DVD drive.
In the root folder of the mounted drive or the E drive, double click the entry named Setup.exe. This starts the Windows installer and replaces existing OS files with those from the ISO. In Windows 11 Build 25905 and higher, there's a Windows Update-based alternative available via Settings > System > Recovery > Fix problems using Windows update. From there, click the Reinstall now button.
The remainder of the process follows the typical behavior when installing Windows. After the first reboot, the current OS will no longer be accessible. Administrators should follow the same steps a clean install.
How to boot from Windows Media as a clean install
The approach to applying ISO files involves loading them onto bootable media. Usually this involves some type of USB-attached storage device, such as a flash drive; an SSD, or solid-state drive, such as mSATA or M.2 NVMe; or a hard disk. With the help of the media creation tool, desktop administrators can create USB bootable media, or a third-party alternative such as Rufus or YUMI.
There is another option that involves no media creation step. Rather, Ventoy creates a small 32 MB bootable Extensible Firmware Interface (EFI) partition. This starts the PC up, then displays all ISO files in a second partition named Ventoy. Pick one, and the software then boots the PC into the chosen ISO.
Sometimes, admins need to start over from scratch when installing Windows on a PC. This process begins with reformatting the system or boot drive so that it gets brand-new partitions. The same thing is necessary to create such partitions for the first time on a new PC that's never had an OS installed -- known as a bare metal install. The operation is known as a clean install because it creates a brand-new disk structure.
In Windows 11, a clean install creates several partitions by default:
- The boot partition. This is usually labeled EFI on PCs newer than 2017 and master boot record on older machines. This is where the normal Windows boot process begins. A similar partition will be written to bootable media so it can boot a PC.
- The Microsoft Reserved Partition (MSR). This small 16 MB partition helps with general partition management.
- The Windows OS partition. This takes up most of the drive -- its sections are usually labeled Boot, Page File, Crash Dump, etc. -- and a recovery partition that is 600 MB to 1 TB. Figure 3 shows this layout without the invisible MSR via Windows 11's built-in Disk Management tool.
When bootable Windows media starts up a PC, it runs WinPE, a special, slimmed-down version of Windows. This has enough smarts to run the Windows Installer -- Setup.exe -- to get Windows installation going, or it can invoke a slightly more powerful but still lightweight image named the Windows Recovery Environment (WinRE).
For newer Windows PCs, administrators might need to turn off secure boot in the BIOS to enable the machine to boot from bootable Windows media. This will be necessary if the administrator interrupts the normal boot process and get a boot drive menu that does not include an entry for your bootable device. You'll need to consult the BIOS or EFI manual as well as help info from the user's or operator's manual. These are usually available online by visiting the maker's website and then searching for the make and model, such as Lenovo ThinkPad P16 20LH0028US for this example's current test machine. To access the BIOS, administrators can click through Settings > System > Recovery > Advanced startup, then click the Restart now button.
Save all work and exit any important applications beforehand, because this restarts the PC immediately.
How to run Windows Recovery Environment
When an administrator starts up from bootable Windows media, you'll see a screen as shown in Figure 4. To get access to Windows Recovery, click the Troubleshoot option on the bottom left of the screen.
When you select Troubleshoot, a new options screen appears. It allows users to choose between Reset this PC -- reinstall Windows, with or without existing personal files from the Users folder in the C drive -- and Advanced options.
If the admin selects Advanced options, a corresponding menu will appear. This offers options to make startup repairs, change startup settings, access a Command Prompt Window, uninstall updates, access UEFI firmware settings or revert to a restore point.
Over and above Windows installation, WinRE offers access to startup repairs and settings. Access to the Command Prompt means that any command known to Windows may be run against the Windows image on the now-quiescent system drive.
This permits almost arbitrary introductions of or modifications to existing files and folders within the C drive image. Uninstall Updates uses the Deployment Image Servicing and Management command in the background to allow users to uninstall recently applied updates to undo their changes. This was a key aspect in fixing the recent CrowdStrike debacle, for example. UEFI firmware settings provide access to the PC BIOS, while system restore invokes system restore points where available.
Ed Tittel is a 30-plus year IT veteran who has worked as a developer, networking consultant, technical trainer and writer.
