I know that partitioning takes place on teh SD Card, however, I was not aware that performing a wipe of the system did not wipe the system files. I guess the confusion is largely due to how that option is labeled.
So when you preform a system wipe, what is affected? User settings/data not stored on the SD?
When you perform (in Amon_RA) a "Wipe data/factory reset", the data and cache partitions are erased. The data partition contains a bunch of stuff, including all application settings, and usually application data too - depending on the app design.
Applications have the freedom to write stuff to the SD card, but generally only do that if their "data" tends to be large (music files, photos, ringtones, large databases). Usually 100% of the application "settings" are stored in the Eris' system flash memory (not the SD card).
There are 6 "official" partitions in the Eris' (system) flash memory: recovery, boot, system, data, cache, and misc. (In addition there is 43 Mb of "unaccounted for" flash memory which probably contains the bootloader (0.5 Mb), radio firmware (16Mb), and other mysteries)
The version of Amon_RA that is on the Eris:
- when performing a "Wipe data/factory reset" only cleans these two: data and cache
- when performing a Nand backup, only copies these: boot, system, and data.
- when performing a Nand+ext backup, only copies these: boot, system, data, and (SD card) ext
boot: contains the kernel and a small number of files including initialization scripts
system: contains all the pre-installed apps plus all the native code and libraries for the ROM
data: contains application data and settings, Dalvik-cache, and other system support
A ROM developer has the flexibility to install files to the recovery, boot, system, data, cache, misc, radio, and even the SD card; but typically they only write files into the system partition.
Every time Android boots, it does some housekeeping to make sure that there are folders set up in /data, and unique accounts assigned to every app, and so forth - so if the "data" partition happens to be wiped clean, it will set up the right stuff in there so that when the apps run, they will each have their own private areas in there to store application settings and private or shared data. It also builds up the "Dalvik cache", which is also in the /data partition. That's why the first time you boot Android after a factory reset, or a "wipe + ROM install", it takes longer to boot than subsequent times - and also explains why applications get reset back to their default settings.
Long explanation; I hope it helps
eu1