They are automatically downloaded and applied on the fly to fix the Windows recovery environment (WinRE), set up binaries, or any files that the Windows setup uses for feature updates.
Then comes the Dynamic Updates (DU) that are meant for the Windows setup engine. Unlike the SSU, they're distributed separately from the regular CUs.Windows Feature Experience Pack is yet another type of update that delivers new feature improvements to customers outside of major Windows feature updates.
In that case, always install/integrate the SSU before engaging with the CU. Power users or system admins may still prefer to deal with the CAB variant for ease of deployment. The servicing stack is the code that installs other operating system updates, which is why Microsoft usually bundles them with CUs before publishing a standalone MSU package. In some cases, you might need to apply a Servicing Stack Update (SSU) before installing the next CU.
