I presume [your Hyperdrive 20] does not require a special software driver?
To be honest, I've never checked the contents of the System Folder on that drive to see. I will need to do that check and report back.
As for being HFS compliant, wouldn't that be up to the System? I mean the HD20 loads the HFS code into RAM as the system boots.
My HyperDrive 512 does not load the HD20 INIT at boot time. I guess that is why it cannot have HFS partitions. So without having checked the contents of my System Folder on that HyperDrive, I can only assume that the code required to make the HyperDrive boot is in the two ROM chips on the
HyperDrive Controller Board.