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A few years ago, this author reviewed several Windows tablets for another publication, and only one of them had more than 32GB of storage. While it was an interesting concept, this ultimately wasn't a credible amount of space for a device whose operating system would occupy about 20GB.

At the time, even an iPhone with 16GB of storage was more generous, because iOS took up relatively little space. None of these tablets ended up creating much of a market, and their limited storage was likely one of the main reasons (the other being that Windows still didn't adapt well to a touchscreen interface).

SEE: How to clean out junk files in Windows 7, 8.1, and 10

However, Windows tablets and laptops with limited storage have remained common enough over the years for Microsoft to remind people how sizeable Windows is, as it closes in on a major update to Windows 10 next month.

Since updating to a new version of Windows requires about 10GB of storage space, and about 20GB of a 32GB drive may already be occupied by the operating system, you may be forced to remove pretty much everything you've put on your device, if it's compatible with the big update coming to Windows 10 next month.

Microsoft is also warning users that Windows Update literally does not verify that enough space is available before commencing. So if the device runs out of space while updating to the next version of Windows 10, the installation simply fails -- and it may not be recoverable. Your data may still be on the drive, but Windows itself is hosed and must be fully reinstalled.

Most users are not familiar with the process of installing Windows -- it simply comes on the laptop or desktop that they've purchased from the store. This device may come with a recovery disc, but those are easily lost.

Making matter worse, a lot of these Windows devices with limited storage may not be set up to allow OS installation from an external USB drive either. In our experience, the available paths around this problem are not easy for the average user to tackle, even with guidance.

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If you're lucky enough to have 64GB or more, Windows can still bloat to fill that space, as you download periodic system updates, install apps, create save games, and fill up your browser cache. Unless you stay on top of it, it can become a real problem.

Thankfully, Windows has a number of built-in tools to remove clutter, and we have them all documented right here with step-by-step instructions.

In our experience, the biggest culprit of lost storage space is Windows Update itself, which has two tricky habits. For one, it keeps a compressed copy of entire previous installations of Windows. These unsolicited pseudo-backups can easily take up as much space as a fresh installation of Windows. Two, the installers for previous security patches may also be retained, taking up several more gigabytes.

If you follow our junk file removal guide, and you copy your important files over to another device before you download the big Windows 10 update next month, you'll probably be fine. But a significant number of other users may not be so lucky.

The takeaways

  • As we approach the big Windows 10 update coming next month, Microsoft has reminded users with limited storage space that they may want to clean out junk files beforehand, because Windows Update will not confirm that you have the necessary space before proceeding.
  • Updating to a new major version of Windows usually requires about 10GB of free space.
  • We have a full step-by-step guide to cleaning out junk files in Windows, if you're not sure about making the cut.

Also see

Tom McNamara is a Senior Editor for CNET's Download.com. He mainly covers Windows, mobile and desktop security, games, Google, streaming services, and social media. Tom was also an editor at Maximum PC and IGN, and his work has appeared on CNET, PC Gamer, MSN.com, and Salon.com. He's also unreasonably proud that he's kept the same phone for more than two years.