Windows 10 update: How to recover your data lost during OS upgrade

Some users of Microsoft's Windows 10 had found some program files went missing from their computers after updating to the latest version. The trick to recovering these files is to re-install them or bring them to the local drive from the old backup.

In a blog post, in tech tutorial site, HowtoGeek, the writer explained that users can get their lost program files by re-installing them in the updated PC.

"If you run into this problem, and you want to get the program back, just reinstall it. In most cases, this will involve re-downloading the program from its developer's website. You'll probably be downloading a newer version of the program than the one that Windows uninstalled, so it may just work without any hassle," the blog explained.

The post said missing files are not a usual concern because it occurs only during major updates with a lot of upgrades and fixes. The incidents of missing files came to light in November 2015, when the company released the first major update for Windows 10.

"Windows won't just remove programs at random times. It will only remove programs when upgrading to a new major version, or "build," of Windows 10. That's because these major versions, or "builds," are treated differently from normal Windows updates. Builds of Windows 10 — like the fall update, Windows 10's first big update — aren't like normal Windows updates or service packs at all. Instead, they're more like upgrading to an entirely new version of Windows."

However, during the update, the new OS creates a backup directory of the old data on the system drive (also called drive C) of the computer named "Windows.old" and fills in all the old and incompatible program files in it. These files are removed from drive C because they can lead to OS crashes, bugs, or come in conflict with the new OS, making the system unstable and leading to performance deterioration of the entire system.

"That's usually C:Windows.old. This is also displayed as "Previous Windows installation(s)" in the Disk Cleanup application," the blog elaborated.

On occasions when the files do not appear even after re-installing them, another way to get them is to pull the files from this backup directory and save them again to the local disk.