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Microsoft breaks down how it shrunk Windows 11 updates by 40%

Windows 11 Update Checkforupdate Dark
Windows 11 Update Checkforupdate Dark (Image credit: Daniel Rubino / Windows Central)

What you need to know

  • Microsoft has revealed the secret behind its ability to shrink Windows 11 update sizes by 40% as compared to the size norms of previous operating system updates.
  • The methods employed by Microsoft are very technical.

Microsoft says its Windows 11 update sizes are 40% smaller than what the company's operating system updates used to be. Curious how the tech giant has managed such a feat? Well, after reading the explanation, you may have more questions than answers, as well as a desire to get an advanced computer sciences degree.

In the blog post (opens in new tab) where Microsoft reveals its methodology, we find out the secret sauce is "reverse update data generation." As to what that is? Well, you'll have to read the post yourself to find out, possibly in addition to some textbooks on data transmission. Here's a sample of Microsoft's explanation as to what would've constituted a non-viable approach in the pursuit of 40% size reduction:

Binary deltas utilize transforms and patching instructions to transform a file from its base version to a target version. While some patching and transforms that add data to a file are non-destructive, transforms and patches may delete data needed for a reverse delta. For this reason, a bidirectional delta would need to store the content added in the forward delta and the content deleted during the forward apply. Because the data in forward and reverse deltas are largely disjoint, little efficiency is gained from a bidirectional delta over paired forward and reverse deltas.


Source: Microsoft (Image credit: Source: Microsoft)

If none of those words make a lick of sense to you and you're not familiar with topics such as the hydration of target revisions, you may be out of luck. But for those who do get this stuff, perhaps Microsoft's post makes for an interesting read.

Robert Carnevale is the News Editor for Windows Central. He's a big fan of Kinect (it lives on in his heart), Sonic the Hedgehog, and the legendary intersection of those two titans, Sonic Free Riders. He is the author of Cold War 2395. Have a useful tip? Send it to

  • In a nutshell: updates used to contain data that describes how files should be modified for upgrading (Windows Update) and downgrading (i.e. Windows Restore/rollback). What they did instead, is during the update process the PC essentially records the steps (file modifications) needed and can apply the inverse of those in reverse when needing to downgrade. Thus they don't need to transmit the data that describes how you can downgrade, as that is essentially generated during the update process on your PC.
  • That's very interesting and cool!
  • Thank you for the explanation.
    Cheers 👍
  • so, finally, MS introduced Deltas, only a decade or more after Linux used it.
    better late then never, he?
  • Nope, they used deltas ever since there were updates too. They reduced the size of the updates by not including the reverse delta in the download, as it's calculated on your PC instead from the forward delta. Linux doesn't have reverse deltas at all AFAIK.
  • Does that mean that Linux doesn't support uninstalling or rolling back an update?
  • It supports downgrading, yes.
  • There's always gotta be one who tries to sink the boot into Microsoft without any clue what they're talking about. Using Linux doesn't actually make you smart.
  • Best comment so far. "Using Linux doesn't actually make you smart." :-)
  • Strawman, congrats on your nonsense take.
  • I got it, there's the old days and the new days and the process to get both to move and stay on the sustenance but the autoclave just makes it neat illegible... Simple.
  • Microsoft was never good at communication.
  • This was posted on the Windows IT Pro Blog, so not aimed at your average moron or even your slightly more clued in moron. It was aimed at people who understand technical terminology and, quite frankly, would probably have an issue if the information were dumbed down.