Microsoft promises drastic cuts in disk space use for Windows 10

The increasing popularity of SSDs and flash-based storage have created a big problem for Windows, and that problem is getting worse as OEMs shrink storage on cheap tablets to save costs. To address the problem, Microsoft is making some radical changes in Windows 10.

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With Windows 10, Microsoft is belatedly addressing a storage crisis that has been years in the making.

In a blog post published today, Microsoft confirmed that it is actively working on reducing the disk footprint of Windows 10, leaving more space for data. The changes involve compressing Windows system files (an option that was added without explanation in Windows 10 Preview build 9879 and is available in the Disk Cleanup utility in current builds). It also plans a drastic redesign of the way recovery images work.

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Microsoft's example space savings (in green) for 64-bit Windows 10
In the example Microsoft used in today's blog post (accompanied by the pie chart shown here), the changes would cut the disk footprint for Windows system files by as much as 45 percent.

Before getting into the details, a little history is in order.

For more than 15 years, the storage corollary to Moore's Law was Windows' best friend. Each new version of Windows required more disk space, but hard disks were growing in capacity (and offering faster read/write speeds), so the bloat didn't matter all that much.

Then things changed, gradually but inexorably, as solid-state storage began to displace conventional spinning disks.

Solid-state drives (SSDs) began appearing in high-end notebooks around the time Windows 7 was released. They offer dramatic performance improvements but cost significantly more than conventional hard drives. SSD prices continue to decline year over year, but on a cost-per-gigabyte basis they are still far more expensive than conventional disk drives.

The rise of small, cheap Windows tablets, designed to counter the rise of cheap Android devices, has exacerbated the problem. These devices use flash memory (which is slower than SSDs but still much faster, smaller, and less power hungry than a hard disk) and often include total storage of 32 GB or even 16 GB.

And one of the signature design changes in Windows 8 and its successors has also been a contributor to the problem. Every new PC shipped with Windows and 8.1 preinstalled is required to include a recovery partition that contains an image of the originally installed operating system. The size of that partition is determined by the PC manufacturer.

Here, for example, is what you get with the entry-level Surface Pro 3, with a Core i3 processor and a 64 GB SSD. Note that roughly 10 percent of the total storage capacity is occupied by the recovery partition at the far right, which is only used to restore the system to its original configuration and represents wasted space under normal conditions.

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For the latest generation of Windows 8.1 tablets with more limited storage, Microsoft devised a solution called Windows Image Boot, aka WIMBOOT, which allows the recovery partition to do double-duty as the system partition. This Dell tablet has a total of 32 GB of flash storage (don't get me started on why the Disk Management utility insists on displaying that number in a way that doesn't match how storage is advertised), but the WIMBOOT partition takes up a third of it, leaving less than 20 GB of space for data files.

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To solve the problem, Microsoft is working on two major changes to Windows 10. First, Windows can efficiently compress system files. According to Microsoft, that results in a net increase in free space of roughly 1.5 GB on 32-bit systems and 2.6 GB on 64-bit installations. (Windows 10 phones will also reportedly be able to take advantage of this compression algorithm.)

When I tried this option on a Surface Pro 3 using Windows 10 build 9926, the Disk Cleanup utility said I could expect to recover 2.5 GB of storage. The actual amount of extra space available after the Disk Cleanup operation completed was 4 GB.

Second, and more importantly, Windows 10 will do away with the separate recovery images that waste so much space, recovering an additional amount of space between 4 GB and 12 GB. And that redesign of the Refresh/Reset functionality has another significant advantage:

Without a separate recovery image, the Refresh and Reset functionalities will instead rebuild the operating system in place using runtime system files. Not only does this take up less disk space, it also means you will not have a lengthy list of operating system updates to reinstall after recovering your device.

Finally, Microsoft says it's making WIMBOOT unnecessary going forward. The initial iteration of this feature in Windows 8.1 was messy and required OEMs to use a special install process. It also made it impossible for third-party utility developers to work with WIMBOOT images. Microsoft says the system compression changes it plans to add in future builds of Windows 10 will use the standard install process, making it possible for more systems to incorporate compression.

According to Microsoft, these improvements in storage utilization will be available for upgrades as well as with new OEM installations. Most desktop PCs and conventional laptops should qualify. Smaller devices with limited RAM or underpowered CPUs might be blocked if a "suitability assessment" determines that the benefits of compression would be outweighed by the resulting performance drag as the system struggles to compress and decompress files.

Microsoft has yet to solve a Windows 10 upgrade challenge on small Windows 8.1 devices that use the WIMBOOT feature. Those devices typically have limited storage (32 GB or less). Currently, those systems are blocked from Windows 10 upgrades because there simply isn't enough room to handle the downloaded Windows 10 image while still allowing for a graceful recovery if something fails during the upgrade process. "We are evaluating a couple of options for a safe and reliable upgrade path for those devices," Microsoft says.

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