My Windows directory is currently sitting at 49GB. I don't think this is a realistic idea for Windows-based PCs unless cheap SSDs start getting bigger with a quickness.
But the ideal solution would be a copy-on-write filesystem supporting snapshots, rather than A/B partitions.
NTFS is already that via Volume Shadow Copy. They just don't use it in the way we're discussing, but the tech is there.
That doesn't sound like how much Windows is actually using for itself. How much of it is \Windows\Installer\?
I assumed it WinSxS related as the other reply mentions, and upon investigation found that it is 9GB alone! I don't run Windows outside of work so I've just never really bothered looking into it, but if it continues to balloon I guess I'll have to.
I know in the past, any Windows updates would be cached in your windows directory forever and there was no safe way to remove them. That would gradually grow the windows directory size forever. Also, it seems there are a lot of files that get thrown in there when you start installing multiple versions of SQL Server or Visual Studio.
Disk Clean-up.
Clean-up System Files.
Windows Update Clean-up (and Temporary Windows installation files).
Ok. Ok.
Enjoy.