All of the previous generations of Raspberry Pi contained all of their firmware on the SD card. Starting with the Raspberry Pi 4 the device actually has onboard upgradable firmware stored on an EEPROM chip separate from your storage. Updating this firmware is very important as one of the first released updates reduces power usage of the Pi by 30% which also reduces how hot it gets.
In this guide I’ll show you how to update the bootloader firmware (no, it’s not apt-get upgrade, it’s a new utility called rpi-eeprom!) and also show you how to make a recovery SD card if your firmware gets corrupted and needs to be reflashed.