"Initializing..." WU download metadata cab files, process them, calculate needed files to download "Downloading.." WU download needed files (edition esd, LP cab, WindowsUpdateBox.exe , *_psf.rng) "Praparing to install.." 0 - 50 % WU generate the actual new os files "Praparing to install.." 50 - 100 % WindowsUpdateBox.exe starts to deploy and prepare new os
I was describing Express UUP process Canonical UUP doesn't require or use delta files the processing merely to determine which .ESD/.cab files to download as-is i don't know how or when WU decide to use Canonical or Express UUP