Here are a couple of diagrams of the boot process.

1. at reset, push first bootloader into external RAM then reset eZ80 to start first bootloader
2. first bootloader loads second bootloader/disk manager/disk operations binary from microSD
3. second bootloader mounts virtual disks for drives A and B, loads CP/M from reserved tracks of drive A, jump to BIOS coldboot entry point
4. CP/M running, virtual disk access provided by BIOS and mixed-memory mode disk I/O function

The limited amount of flash in the Z8 drives the need for two bootloaders. The largest Flash for an 8-pin Z8 is 8KiB.  The desire to keep the µP and µC Zilog drives the Z8 and the board size drives 8-pins.