Xbox:EEPROM

Before modifying your Xbox permanently (softmod or hardmod), it's recommended to backup your EEPROM and optionally your C: drive. A backed up EEPROM will allow you to access a locked hard drive on a PC or with Chimp if you are using a softmod or are keeping your hard drive locked on a hardmod. Backing up your C: drive will allow you to restore your hard drive to it's original state if something goes wrong.

It is highly recommended to FTP the backups to your PC for safe keeping.

Backing up your EEPROM (Installers)
With Xbox Softmod Tool, an EEPROM backup will automatically be made and placed in E:\backups. Softmod Installer Deluxe (SID) and installer discs have "Backup EEPROM" and "Backup C Drive" options, which will make a backup in E:\backups.

Backing up your EEPROM (EvolutionX)
Navigate to System Utils → Backup. Selecting this will backup of your EEPROM, on-board Bios, HDD Password, and HDD config and place it in C:\Backup\. If your dashboard is not installed on the C: drive, it may not work.

Backing up your EEPROM (ConfigMagic)
Press Start to enter the application, then Start again to open the main menu. Select "Create Backup Files". This will create an EEPROM backup on the E: drive. Most actions in ConfigMagic will make a backup of the EEPROM on the root of the E: drive.

Backing up your EEPROM (PiProm)
In the event that you cannot boot into the Xbox to backup your EEPROM, you can use a Raspberry Pi and three wires to dump it from the chip directly. A full guide can be found on the PiPROM page.

Backing up your C: Drive
For softmodding, it's recommended to FTP into your Xbox and copy everything from the C: drive onto your PC. If something goes wrong on install, you can use your EEPROM backup to open the drive with XboxHDM and put the files back onto it.