Well each pass controls a portion of the installation. From an high level XP perspective, the windowsPE pass is very similar to the TextMode portion. Most of the it's settings involve formatting, OS file copy, all the things that happen prior to the first reboot. Other passes control other portions of the install and some passes are only used during special situations. For instance the Audit passes are commonly skipped by vanilla unattended DVD's, but anyone running sysprep will use them.
You mention how some settings are duplicated and on paper it appears that way, but that is not the case. A few days ago a user was having trouble specifying domain cred's for his WDS installation (using the oobeSystem domaincred), but the problem was his error occurred during the windowsPE portion. For his installation we needed to provide the credentials twice, once during the windowsPE pass (to connect to the WDS server), and the second time during oobeSystem pass to join the new machine to the domain. So these are not really duplicates, but two distinct settings with different uses. You will find this is the case with most of the duplicated settings.
Here is quick rundown of what a normal DVD installation goes through . (i'm missing the second reboot, not sure where exactly that happens)
1) windowsPE pass occurs
2) offlineservicing (if enabled) occurs - followed by reboot. - this is end of the boot.wim session
3) After reboot - Specialize pass
4) Finally the oobeSystem
5) SetupComplete.cmd occurs last (if using $OEM$)
6) First login occurs - desktop appears.
on a sysprep installation, two more audit passes can occur between 3 and 4. (there is also a generalize pass that I think occurs before #3)
This is a lot to cram into a little post. Ask questions if you have any.
@ Max, what do you think about hosting a pair of WDS compliant XML's. Arwidmark posted some samples for Vista WDS
at this site, but they might need some minor tweaks for W7/WDS
This post has been edited by MrJinje: 11 May 2010 - 07:19 PM