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+FFS usage on Compal phones
+==========================
+
+All Compal phones (Motorola C1xx and Sony Ericsson J100) use a flash file system
+(FFS) structure for user data.  On all currently known models with the single
+exception of Mot C155/156, this FFS is in our familiar TIFFS format - see the
+TIFFS-Overview article.  Mot C155/156 uses a different FFS implementation with
+a completely different and incompatible on-flash format; it appears that the
+name of this C155/156 FFS implementation is FMGR, as evidenced by the strings
+found in the firmware image.
+
+The location of FFS within the flash on various known models is as follows:
+
+* On Mot C11x/12x phones with 2 MiB flash, the FFS is at 0x1F0000, using 6
+  sectors of 8 KiB each;
+
+* On Mot C11x/12x phones with 4 MiB flash, the FFS is at 0x370000, using 3
+  sectors of 64 KiB each;
+
+* On Mot C139/140 and SE J100 phones (4 MiB flash), the FFS is at 0x370000,
+  using 5 sectors of 64 KiB each;
+
+* On Mot C155/156 phones (8 MiB flash), the FFS is at 0x700000, using 13
+  sectors of 64 KiB each - but the format is FMGR, not TIFFS!
+
+In *all* of the listed cases, this FFS (be it TIFFS or FMGR) is used *only* for
+user data, and not for anything essential.  On all of these phones you can get
+in with fc-loadtool (our raw flash manipulation tool), erase the flash sectors
+belonging to the FFS, exit fc-loadtool and boot the phone's regular fw with
+totally blank FFS sectors - the fw with do a fresh FFS format (it even displays
+a message on the LCD as it does so), and then the phone will function completely
+normally, but be "brand new", without any previous user data.  Compal's
+firmwares also do the same thing (automatically reformat the FFS on the first
+boot, blowing away any old one) if you reflash from one fw version to a
+different one, even if you don't erase the FFS sectors explicitly - Compal's
+FFS stores the fw version that created it, and when their fw boots and sees
+that the FFS is from a different version, they automatically do a full reformat.
+
+The fact that the FFS on these Compal phones is strictly non-essential and can
+be trivially blown away and recreated implies that it does NOT store any vital
+data: no IMEI, no RF calibration values.  Instead the IMEI, the RF calibration
+values and a bunch of other records which we are not able to understand are
+stored in a completely different flash data structure of Compal's own invention:
+see our Compal-calibration article.
+
+Language reset
+==============
+
+There is, however, one additional issue which you need to be aware of if you
+are going to erase the FFS and have the firmware reformat a new one: when the
+firmware formats and writes a new FFS, the UI language is set to the firmware's
+default, and in some fw versions it is not English.  (Both Motorola and Sony
+Ericsson firmwares have "language pack" and "flex" parts in addition to the
+main fw body proper.)  Something one can get lucky and the default fw language
+is English, other times the default language is non-English but still
+intelligible enough to navigate through the menus to change it to English, but
+I got one C118 on which the default fw language is Chinese, and I had no luck
+in navigating through the menus to change it to English.  On that phone I had
+to flash back the original FFS which had the English UI language setting.