3DS:System files

This is a list of important system files or other data.

Filename	Name in essential.exefs	Path in GodMode9	Purpose	Importance
LocalFriendCodeSeed_B	frndseed	1:/rw/sys/LocalFriendCodeSeed_B	Used to identify the console for online play.	Bans from online play are effectively bans on the LFCS. (Don't ask here or NH for help on how to get unbanned.)
HWCAL0.dat and HWCAL1.dat	hwcal0 and hwcal1	S:/ro/sys/HWCAL0.dat and S:/ro/sys/HWCAL1.dat	Contains hardware calibration data. Parts of this are put into the Config savegame during first-time setup.	If this file is lost or taken from a different console, then when the console is formatted, the calibration data will be inaccurate and can result in problems such as flickering screens.
movable.sed	movable	1:/private/movable.sed	Contains data that is used to encrypt digital games and saves on the SD card. Also used for CMACs on various NAND files.	Keeping a backup of this is important if you want to ensure you can still recover your old saves if your console is lost or broken!
NAND CID	nand_cid	M:/nand_cid.mem	Used as part of the NAND encryption.	This can be used to decrypt a NAND backup on a PC, however it's not strictly required for 99.9% of cases.
NAND header	nand_hdr	S:/nand_hdr.bin	Contains information on the NAND partitions. The console-unique part here include the TWL MBR, which is encrypted per-console.	Corrupting this will prevent the console from starting. However GodMode9 can generate a new one in its place if you can use it through something like ntrboot.
OTP	otp	M:/otp.mem and M:/otp_dec.mem	Contains various kinds of console-unique data. Used to generate encryption keys and identifies a console in some cases like the eShop. See also: 3dbrew:OTP Registers	This is required to decrypt a NAND backup on a PC. Sharing this means someone could impersonate your console to Nintendo, so don't post it in a public space!
SecureInfo_A or SecureInfo_B	secinfo	S:/rw/sys/SecureInfo_A or S:/rw/sys/SecureInfo_B	Used to identify the console in some cases like the eShop.	Sharing this means someone could impersonate your console to Nintendo, so don't post it in a public space!

Notes

GodMode9 does not automatically update the essential backup; to manually update it, choose a NAND image (either SysNAND, EmuNAND, or a backup on the SD card), then choose "NAND image options..." -> "Update embedded backup".

hwcal0 and hwcal1 were not included in essential.exefs before GodMode9 v1.3.0 (August 7, 2017 (2017-08-07)).