For those running, or taking care of, Win10 installs that boot from hard disks, here’s a trick worth knowing. In Win10 compact OS for conventional HDs speeds up performance. On machines that boot from SSDs, however, Win10 disables this function by default. That’s because HDs are slow enough that compressing the OS files leans on the CPU for decompression. The speed gain from reading less data from a slower disk offsets the performance loss from decompressing that data before putting it to work. But SSDs are so fast that this trade-off is no longer favorable. That means a slight net performance loss vis-a-vis reading the data uncompressed. But for setups with small SSDs (or slower, flash-based storage devices like eMMC) this command might also prove useful because it does free up storage space and won’t impose a heavy performance penalty.
How to Query Win10 Compact OS Status
One simple command does this nicely at the command line. I show examples from PowerShell, but it works just as well in an Administrative Command Prompt windows (cmd.exe), too. Here’s what the command and its output look like from machines with the OS compacted or not:
Above: compact OS turned on; Below: not turned on, with explanation.
Anyone with admin privileges can turn it on or off easily.
The /compactOS:query parameter simply checks status.
[Click either image to see full-size view.]
To learn to use the compact command, see the MS Docs compact page. It’s easy to check status, and to turn it on or off. By default, it turns it off for PCs that boot from SSDs. I no longer have any PCs that boot from spinners, so I can’t say if Win10 is smart enough to turn it on by default for such rigs. But it’s easy enough to check — and change. If you’ve got some, either or both activities should pay worthwhile dividends for those PC’s users. Enjoy!