Windows インストールファイルの肥大化、Copilot+ AI が原因か

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ZDNET's key takeaways

• Microsoft's Windows installation files have ballooned in size.
• In the last 10 years, the download has doubled to more than 8 GB.
• The most likely cause is Microsoft's AI files for Copilot+ PCs

Windows downloads are bigger than ever. I noticed this a few times over the past six months ("Huh, I don't remember a download being this big before") but hadn't had time to dig into the details.

Then I saw a recent post from Michael Niehaus titled "How can Windows 11 keep getting bigger?" and I realized, no, it was not my imagination.

Also: Microsoft goes all in on new AI-powered Windows security strategy - what it means for you**

Just how big are these downloads?

Here's Michael's chart showing the increase in size for multi-edition downloads from Microsoft's Visual Studio (subscription required). The first value is from the initial release of Windows 11 version 24H2 in November 2024 up through the latest version 25H2 from July 2026. (Because 25H2 was delivered as an enablement package for 24H2, both releases are from the same branch.)

*Windows deployment expert Michael Niehaus has been charting the growth of Windows installer ISOs Michael Niehaus*

As Michael notes, almost 6,000 new folders and over 20,000 new files were added over that stretch of less than two years.

I went through some additional ISO from my collection to plot the change in download size since the initial release of Windows 10 in 2015. See for yourself.

*Those ISO files have been getting bigger since the first release of Windows 10 Ed Bott/ZDNET*

Even using the Media Creation Tool to download the latest ISO doesn't help. That file is still a humongous 6.8 GB, nearly twice the size of the original Windows 10 release.

Also: Microsoft's new Windows 11 recovery tool is the ultimate Undo button - how to enable it

Michael's findings deserve extra weight, given his background. He spent 16 years at Microsoft working on just about everything to do with Windows deployment. I learned a lot from him, and if you ever had "deploy Windows machines in a business" as part of your job description, you probably did, too. (He's still in the same business, working for the Swedish company 2Pint Software.)

Is this just evolution, or is it bloat?

I'm always reluctant to use the term "bloat" to refer to Windows, because people have been complaining about Microsoft's bloated software since the days of MS-DOS. I wrote about it 20 years ago -- Windows bloat? It's always been that way. My favorite is probably this review of Windows XP, which called it...

a monstrous, bloated brute that requires a state-of-the-art PC and two gigabytes of hard disk space before it will even say 'hello'. This means any consumer foolish enough to want to run XP will probably have to buy a new PC.

Two gigabytes of hard disk space? It seemed like a lot back then.

But maybe this time is different. In the past, Microsoft and its OEM partners could solve the problem by throwing more hardware at it. Given the massive price increases in memory and storage that are likely to persist for years, the "just add hardware" option is no longer feasible.

Also: Why your RAM options cost 4X more now than last year

The biggest weak spot is system storage. Microsoft's official requirements for Windows 11 call for a minimum of 64 GB for the system drive. Just for fun, I put together a virtual machine using a virtual drive that size and installed the latest release of Windows 11 on it. It reached a peak storage usage of 28.2 GB before it finished installing Windows and the latest updates. That's roughly half the size of the drive, before installing any apps or saving any user data files.

Where's the bloat coming from?

I wasn't sure exactly why this was happening, so I chatted with Michael to see if he had any ideas. One reason the cumulative updates are so large is that they include a massive amount of AI-related code, specifically 3GB of shared AI models used by various local AI features on Copilot+ PCs. Dig into those files and you'll find dozens of WindowsWorkload.* files dedicated to that mission. If you have a plain-vanilla, no-NPU, Copilot-minus PC, you still have to download these bits, which the Windows installer will then ignore.

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"Is Windows getting bigger? Yes," he told me. "Are updates getting bigger? Yes. Does Copilot+ make it worse? Yes, much worse."

One problem he pointed out is that Microsoft is shipping many of these massive code dumps in the monthly cumulative updates delivered through Windows Update rather than distributing them as system components through the Microsoft Store.

Yes, that's an option. Windows 11 is already delivering some of its most important components that way, reducing the burden on Windows Update and ensuring those updates are delivered only when the underlying app is in use. (They also don't require a restart to complete installation, which is a big win.) Check the Downloads & Updates page in the Store to see examples of system components now managed by the Store instead of Windows Update.

*Microsoft could help by moving some of those humongous AI pieces to the Microsoft Store, where they can be managed more wisely. Screenshot by Ed Bott/ZDNET*

Why does it matter?

These are issues for anyone whose job involves deploying Windows and Windows updates on corporate networks or maintaining Windows PC on smaller business networks.

Also: My 5 favorite Windows Insider features in 2026 so far

The real challenge is for anyone who owns a system with a paltry 64 GB system drive. Microsoft says that's enough to run Windows, but it's hard to imagine how minimal your workload has to be for that installation to make sense. I agree with Michael that 128 GB should be a bare minimum, and anyone doing serious development or creative work needs a terabyte of storage.

Announcing Windows 11 Inside Out, Second Edition

I'm about to deliver the final pages of my new book, "Windows 11 Inside Out, Second Edition," to the publisher. I've been working on it for six solid months, and it's a massive revision that anyone who made it all the way to the end of this post will appreciate. It's available for preorder from Amazon now, and I'll have links to other purchase sites on my website.