It could be done quickly by reading the MFT. WizTree can calculate the size of all 236k directories/800k files on my system in two seconds. For some reason, Explorer takes ~10 seconds to calculate the size of a single directory (Program Files, 17k directories, 240k files). If Explorer just did what WizTree does, it could actually show and sort by directory sizes.
That's because folders have no size. It requires calculating children size recursively.
It could be done quickly by reading the MFT. WizTree can calculate the size of all 236k directories/800k files on my system in two seconds. For some reason, Explorer takes ~10 seconds to calculate the size of a single directory (Program Files, 17k directories, 240k files). If Explorer just did what WizTree does, it could actually show and sort by directory sizes.
You're saying the size of the folder's contents is its size? Wow, that would sure be useful information for a file explorer to expose.