Open and Use Disk Cleanup in Windows 10  

Brink said:

Just note that checking the System Compression box isn't for deleting files, but to only compress them to save the amount of space displayed for it in Disk Cleanup.

Thanks for the info.
Dang it, I will leave it alone then.

MS tech's don't know much more than we do.
I was of the understanding it compresses non essential system files but I could be mistaken.

The compression works extremely well - 85% for windows and 90% for program files - my windows 10 install (including 51 programs) is (just) under 3GB if you exclude page file and user data etc which is smaller than the ISO I installed it from - see here Microsoft promises less disk space Win10 - Windows 10 Forums

Is the system compression option the same as using the command-line function+option:
"compact /compactos"?

So for instance this queries the current state:

Code:

compact /compactos:query

And these commands change the state to be on or off.

Code:

compact /compactos:always
compact /compactos:never

I seem to remember that compactos is only recommended for solid state drives, and indeed the System Compression option doesn't appear in Disk Cleanup on my old laptop with spinning disk.

Thank you!