Microsoft announced in April that installing the Windows 10 May 2019 Update would require at least 32GB of available storage. That's a marked increase from previous versions of Windows 10, but today the company clarified that the 32GB requirement is only for new devices from its OEM partners.
Previous versions of Windows 10 required varying amounts of available storage, depending on whether you're installing the 32-bit or 64-bit version of the operating system. For the Windows 10 October 2018 Update, for example, installing the 32-bit and 64-bit versions required a respective 16GB and 20GB of available storage. The most recent update doubled (for the 32-bit version) Windows 10's storage requirements.
Initially, it wasn't clear why the Windows 10 May 2019 Update required more storage than its predecessors. But new support documents from Microsoft explain that much of the increase stems from the Reserved Storage feature, which is enabled by default on clean installs and devices with the most recent version of Windows 10 pre-installed, but which isn't automatically enabled when upgrading from older versions of Windows 10.
Microsoft said in one support document that Reserved Storage "sets aside disk space to be used by updates, apps, temporary files and system caches" in an effort to improve "the day-to-day function of your PC by ensuring critical OS functions always have access to disk space." When the company announced Reserved Storage in January, it said the feature would take up about 7GB of storage and people were, predictably, a bit perturbed by that.
Reserving that 7GB of storage accounts for nearly half of the Windows 10 May 2019 Update's increased requirements. Microsoft said in another document that those requirements are really more like guidelines, though, because "PCs that don’t meet new device disk space requirements will continue to receive updates, and the 1903 update will require about the same amount of free disk space as previous updates." Huzzah!
There will probably still be people annoyed that new devices ship with so much of their advertised storage occupied by Windows 10 itself and Reserved Storage. But at least it's clear that users who can't spare a few gigabytes can still install Windows 10 updates, and if Reserved Storage facilitates Microsoft's efforts to improve the Windows 10 update process, losing that 7GB seems like a small price to pay for a bit more sanity in that area.