@Boing-ball I am not happy with what you write. That AmigaOS prefers IDE is only by coincidence. The OS will initialize drivers in the order they appear in the resident modules list. In order to build the resident modules list it will first scan the Kickstart ROM for resident tags and then add expansions from the Zorro bus. Hence mainboard periphals will be initialized before third-party expansions.
Each driver on initialization will scan its hardware for partitioned harddrives and read the partition tables. It will add all partitions into a list to be mounted by dos.library and all bootable partitions into a list of boot nodes, ordered by boot priority. It will also read required file systems from the RDB and add them to filesystem.resource if not already present or present with a lower version.
Therefore if a later driver will encounter a third-party file system on one of its partitions it might benefit from an earlier driver which has already loaded this file system.
Only when all drivers have been initialized, dos.library is started, will mount all partitions from the mount list and start booting from the first node in the boot list. This means that the boot priority does not have any influence on whether a partition is mounted or not, it only determines which partition is used for booting.
Also 5 is in no way reserved for the floppy drive, it is only hardcoded. But nothing hinders you to set your partition to 5, too. It just won't boot because the floppy drive is checked first.
Valid boot priorities range from -127 to 127 while -128 means not bootable. You can indeed set your partition to a higher value than 5 to prohibit floppy booting (you can still select the floppy drive in the early startup menu).
I would always recommend to put the boot drive on the fastest hardware which most likely is SCSI. And I also recommend to use the fastest file system for the boot drive. Actually there is no reason to use different file systems. If you chose PFS as your preferred file system, you should use it for all partitions.
In the special case of the T-Rex using a third-party file system is a bit difficult because the T-Rex does not read file systems from its RDB. Therefore you need a harddrive with a PFS partition on another controller which is initialized before the T-Rex. Which is quite easy if you already have a drive on the internal IDE bus.
You only need to keep in mind that the PFS partitons on the T-Rex will stop working if you remove the IDE drive.
