Among other things, Microsoft has reduced the size of Windows 11 updates by up to 40%. It managed to do this by tweaking the way updates are delivered to PCs. As such, before we get into the fine details of Windows 11’s update process, let’s look at the way updates work on Windows 10 first.
Windows 10’s Update Process
With the launch of Windows 10 version 1809 in 2018, Microsoft decided to ditch the express update downloads in favor of the paired forward and reverse differential downloads. Windows 11 uses a modified version of paired forward and reverse differential updates.
Windows Updates’ Express Downloads
With express downloads, Windows 10 machines only installed the parts of files it was missing to complete the update. The system determined the parts that were missing by comparing the file versions with historical baselines.
To understand this better, let us assume that Microsoft pushed an update to the Photos app on Windows 10 in July. Because Windows 10’s updates come with all the previously released fixes for a particular file, the size of the updates can become enormous if Microsoft starts packaging all the previous versions of the Photos app every time it updates the app.
In our example, to move the Photos app to the July version, the system will generate differentials from June to July, May to July, April to July, and all to the way to the last supported version of the app. Then, Windows will decide which differential to install based on the current version. So, if the current Photos app is from April, then Windows Update will only install April to July differential.
As you can probably tell, generating and keeping track of all these differentials can become intensely resource-hungry. This resource-intensive nature of express downloads can result in PCs with modest hardware taking a significant performance hit. This is where Paired Forward and Reverse Differential comes in.
Paired forward and reverse differential downloads aim to bring the functionality of the express downloads but without the added performance cost.
Windows Updates’ Paired Forward and Reverse Differentials
To make the update process on Windows 10 more resource-friendly, Microsoft adopted the paired forward and reverse differential mode of updates. In the paired forward and reverse differential process, the Windows update comes with both forward differentials and reverse differentials.
Forward differentials are the set of changes needed to get a file or app to the latest version. In contrast, reverse differentials are the set of fixes that are applied to the current version of the app to get the base version. The base version here refers to the version that was pushed out with a major Windows release.
Using paired forward and reverse differentials, whenever there is a new update for an app/file, the system decides which differential to apply. For instance, if the app is a base version, the Windows update process will only apply the forward differential to get the latest version. But if the app is a version that is in between the base and the latest, the update process first applies the reverse differential to get the base version and then applies the forward differential.
On the surface, the paired forward and reverse differential method looks like the same amount of work as the express downloads method. But look closely.
In the express downloads method, Windows generates and packs all the previous differentials with the update. While in the case of forward and reverse differentials, Windows only needs to manage two differentials.
Only having to manage two differentials reduces a lot of overhead, resulting in compact update packages that are easy to download and process. This gives lower-powered PCs a little, if not a lot, performance headroom.
Windows 11’s Update Process
Microsoft has reduced Windows 11’s update size by 40% through the optimized implementation of the forward and reverse differentials.
The problem with Windows 10’s implementation of the paired forward and reverse differentials is the increase in size. Both the forward and the reverse differentials contain possibly varied data sets. These data sets, when combined in one update package, end up making the package bigger than necessary.
To combat this, Windows 11 uses an “observe, re-encode, and store” approach to generate the reverse differential. Let’s, once again, take the example of the Photos app to understand the process works in detail.
On Windows 11, the update packages that Microsoft pushes only have the forward differential to update the base version of the app. During the application of the forward differential, Windows “observes” the changes/fixes that are taking place. The system then takes these changes and re-encodes them in the form of a data set that describes fixes needed to revert to the base version of the Photos app.
Finally, unlike Windows 10’s updates, reverse differentials in Windows 11 are maintained by the machine. So, whenever an update wants to retract an app back to the base version, the PC provides the steps to take.
By using this technique, Microsoft has shaved 40% off Windows 11’s update size, resulting in optimized updates that are easier on the host hardware.
Windows 11 Updates Are Shaping Up to Be Better Than Windows 10’s in Every Way
Windows 11 packs a lot of fixes for Windows updates. Reducing the size of updates by almost half is an excellent step towards overhauling the updates process for the better.
That said, decreasing the size of updates isn’t the only improvement that Microsoft has made. The company has tweaked the way it handles servicing with a bunch of fixes, including substantially decreasing background activity.
