News

Windows 11 Gets 40 Percent Smaller Cumulative Updates

• By Kurt Mackie
• 10/15/2021

Microsoft explained this week that Windows 11 has an improved cumulative update (CU) technology that is said to reduce the CU size by "about 40 percent."

CUs arrive monthly, and include quality and security patches for Microsoft's client operating systems. The "cumulative" term means they contain past months' updates, as well as new updates, so they tend to grow in size month to month. Having smaller CUs arrive promises to save bandwidth, both for Microsoft and its customers. Microsoft has long had a technology that just delivers the changed bits, which are called "differentials," and that's now been improved with Windows 11.

The 40 percent CU size reduction claim can be found in this article by Jonathon Ready, a software engineer and program manager at Microsoft. There's also a longer article by Steve DiAcetis, a member of the Windows fundamentals team. The article by DiAcetis also includes details notable for IT pros using the Windows Standalone Installer tool with Windows 11, as well as language packs.

No More Reverse-Differential Bits
In essence, Microsoft no longer includes the reverse-differential bits in Windows 11 CUs. Instead, these bits get calculated as needed. It's an improvement over the so-called "Express update" technology that was introduced with Windows 10 version 1809.

Years ago, Microsoft had described its Express technology as decreasing Windows 10 download sizes by about 35 percent, based on the use of differential downloads and Microsoft's Unified Update Platform. These Express updates used "differential download packages" where only the changed bits of files get downloaded.

With Windows 11, Microsoft found a way to generate the reverse-differential bits but only in cases where they are needed.

"We discovered that these transforms and patches can be 'observed' by the delta apply step, and efficiently re-encoded into a reverse delta (n->0), obviating the need to distribute reverse deltas in a paired delta approach," Ready explained.

Reverse-differentials are still part of the CU process, but they just get calculated as needed.

"Reverse differentials are still used; however, they are computed during install time on the device," DiAcetis explained. "So, the model of applying reverse + forward still applies."

The forward differentials "are used to bring a base version of a file (i.e., the RTM version) forward to the target revision," DiAcetis added.

Format Change to CUs
Microsoft changed the "internal structure of the cumulative update" to enable the smaller CUs for Windows 11. DiAcetis warned against opening CUs to see what's inside as "this will break in Windows 11."

Windows 11 CUs combine the servicing stack update (used for updating Microsoft's update services) and the CU patches. This SSU plus CU combination has been in effect for Windows Server Update Services and the Microsoft Update Catalog since "February 2021," according to DiAcetis.

The CU format change also affects some of the tools IT pros may use. For instance, the Windows Standalone Installer (wusa.exe) can no longer uninstall "because the combined cumulative update contains the SSU," DiAcetis noted. Moreover, SSUs can't be uninstalled.

IT pros using Microsoft's Deployment Image Servicing and Management (DISM) tool to install "inner CAB" cabinet files "should change your code to perform the online installation with the outer MSU," DiAcetis also indicated.

Language Packs vs. Local Experience Packs
Microsoft has languages packs for its operating systems, but not for all languages. Some languages are enabled instead via Local Experience Packs (LXPs).

Language packs get updated through CU releases. However, the LXPs get updated instead via the Microsoft Store. IT pros need to understand that distinction, DiAcetis noted.

Windows 11 is getting expanded language pack support for 43 languages, up from the 38 language packs that are supported for Windows 10.

Windows 11 also is bringing some good news for IT pros that attach language packs to ISOs. IT pros no longer have to download a features on demand (FOD) component.

"Starting in Windows 11, the language and FOD ISO has been merged, making it easier to add each to your OS image."

IT pros can just add a language to the image and "Windows will automatically add the additional FOD satellites as needed for those FODs already installed," DiAcetis explained.