We saw last time that the unattend file lets you change some Windows configuration settings that cannot be changed after Setup is complete. But one of the things you can't change is the location of the Program Files directory. Many people wish they could relocate their Program Files directory to another drive in order to relieve disk space pressure on the system partition. Why won't Windows let them do this?
Now that NTFS is mandatory for the system volume (it took only 13 years to get there!), Windows itself can start taking advantage of NTFS features.
For example, Windows Update can take advantage of transactions: When updates are applied, they are done as part of a transaction. That way, if something horrific happens in the middle of an update, the entire transaction becomes abandoned and you don't get stuck with some Frankenstein configuration.
Windows Setup takes advantage of hard links. A large percentage of the files installed by Windows are hard-linked to copies in the C:\Windows\WinSxS directory for reasons I do not understand, but the phrase "component store" may be part of it. (This is why asking Explorer for the size of the C:\Windows directory gives a misleading view of the actual amount of disk space occupied by Windows, because Explorer uses a naive algorithm which counts each hard link as a separate file.) Oh, and in Windows 7, the two copies of Notepad are now hard links to each other.
Ah, but one of the limitations of hard links is that they cannot span volumes. Some of the hard links out of the WinSxS directory point into places like
C:\, and this in turn requires that the Program Files directory be on the same volume as your Windows directory.
Sorry for the inconvenience.