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Microsoft recommends in-place upgrades for the migration to Windows 10. It reduces the time needed for the upgrade process because you don’t have to copy user profiles and you don’t need to reinstall programs.
In-place upgrade installs fresh Windows 10 ^
If you are a Windows veteran, you probably doubt if an in-place upgrade results in a Windows installation that is as stable as a fresh install. It has been a common experience with previous versions of the OS that installations start to deteriorate after being used for some month.
The in-place upgrade is a complex process which transfers configurations and applications to a new Windows 10 installation
However, you have to take into account that an in-place upgrade doesn't just overwrite the old Windows installation with Windows 10. Rather, it is a completely new installation where the old Windows installation is moved to \windows.old.
Device driver update, application compatibility check ^
The new upgrade process is complex and begins with an extensive evaluation and inventory of the computer. If the preconditions for an upgrade are met, the system will boot up WinRE and copy the Windows 10 system files to the corresponding drive. At this stage, setup downloads the newest drivers from Windows Update. Admins can also specify a folder with additional drivers.
Also in the case of an application migration, setup does more than just copying registry entries. Setup uses a huge database to verify the compatibility of each application with Windows 10. The database also contains information about the configuration that is required to make the application run properly under Windows 10. These settings are automatically applied during the setup process.
Microsoft provided a detailed description of the in-place upgrade process on the recent Ignite conference during the “Upgrade to Windows 10: In Depth” session, which you can view on Channel 9.
Downgrade to the previous Windows installation possible ^
Another advantage of an in-place upgrade is that you can roll back to the previous Windows installation at any time. This may also happen automatically, for instance, if the first Windows 10 boot up fails. You can also downgrade to the previous Windows installation manually if, for some reason, the new Windows isn’t up to scratch.
Of course, such a rollback is difficult to accomplish after a fresh install because the existing Windows installation is removed and a new (adapted) system image is copied onto the computer. By the way, such modified system images cannot be used for in-place upgrades. Rather, you have to deploy the original install.wim from the installation media with MDT or SCCM.
Scenarios for a new installation ^
Even the significantly improved in-place upgrade, which Microsoft recommends for most migrations, is not suitable for every upgrade. This is particularly true if you use the upgrade as an opportunity to perform major modifications.
The most important reason for a fresh install (wipe-and-load)
Thus, a fresh install is required in the following cases:
- If you move from a 32-bit installation to a 64-bit version (or the other way around) because of problems with drivers and applications;
- If you want to repartition drives;
- If Windows XP or Vista still runs on the PCs;
- If an older Windows has been installed in the BIOS compatibility mode on a UEFI PC and you now want to use the UEFI firmware natively, you have to modify the disk layout (among other things, you have to use GPT instead of MBR). Reasons for working with UEFI could be the usage of Secure Boot or Device Guard.
- If you want to change the language version: For instance, an in-place upgrade from a German to the English operating system version is not possible.
- If you intend to change to a lower Windows edition: In-place upgrades only allow you to migrate to the same or a higher edition, for example Windows 7 Pro to Windows 10 Pro or Enterprise.
- If you are working with a dual- or multi-boot system, if your Windows installation uses native VHD boot, or if you are running Windows To Go.
- If you encrypted drives with a third-party solution and the vendor does not explicitly support in-place upgrades (BitLocker supports in-place upgrades).
In addition to these restrictions, other reasons exist to consider a fresh install. Typically, if you don’t want to continue using a large number of applications, an in-place upgrade does not make much sense.
You might also want to install Internet Explorer 11 on the old system before you run the in-place upgrade to test the compatibility of existing web applications because Windows 10 doesn’t support older versions of this browser.