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SSD with Raspberry Pi 1 / 2 / Zero W
The older Pi family and the Zero / Zero W also support USB booting with a small catch. You still need to have a Micro SD card inserted in the Pi with only one file on (bootcode.bin). This is because these Pis use the older
BCM2835 which is a Micro SD only bootloader.
The good news is that if we put a otherwise blank Micro SD card in there with this file the Pi can boot from USB storage just fine and take full advantage of the increased speed and storage size. Bootcode.bin basically provides the instructions to the Pi telling it how to boot from USB.
First you will format your Micro SD card as FAT32 . FAT32 is the partition type that the Pi bootloader can read and is the same format as the /boot/ partition on a fully imaged Pi card.
Next grab the latest bootcode.bin from the official Raspberry Pi repository at https://github.com/raspberrypi/firmware/raw/master/boot/bootcode.bin
Copy the bootcode.bin file onto your newly created and otherwise blank FAT32 imaged Micro SD card and then insert the Micro SD card back into the Raspberry Pi.
Now connect your USB storage back to the Pi and power it on. The Pi will boot directly from your USB storage device!