The way I understand it, the boot process is thus:
The system tries to boot from SPI. Failing that (which it should because you've never written boot code to SPI), it boots from eMMC (the flash module inside the Pinebook Pro). The uboot on the eMMC is supposed to attempt to boot from SD card before continuing to boot from eMMC.
Old versions of uboot (that came pre-installed on the eMMC) didn't do this reliably. Newer versions do. As far as I can tell, newer eMMC images of certain operating systems come with the newer uboot. (That's what you're referring to as the "OS on the computer").
Here is the boot information on the wiki:
https://wiki.pine64.org/index.php?title=...t_sequence
The system tries to boot from SPI. Failing that (which it should because you've never written boot code to SPI), it boots from eMMC (the flash module inside the Pinebook Pro). The uboot on the eMMC is supposed to attempt to boot from SD card before continuing to boot from eMMC.
Old versions of uboot (that came pre-installed on the eMMC) didn't do this reliably. Newer versions do. As far as I can tell, newer eMMC images of certain operating systems come with the newer uboot. (That's what you're referring to as the "OS on the computer").
Here is the boot information on the wiki:
https://wiki.pine64.org/index.php?title=...t_sequence