Instead of cluttering up another thread here's one for RAMDisk related info.
Last night I was experiencing file corruption when saving Extended BASIC files to my Horizon RAMdisk. The filename was getting copied into the file I was saving, trashing code at seemingly random spots.
As I was putting together an email to Gazoo, it dawned on me that I had removed my Myarc floppy controller from the system. Without the FDC, the VDP memory pointer at 0x8370 was not modified, because there was no need for any floppy buffers.
Well... ROS uses the 0x8370 pointer to determine where to copy its last used filename and corresponding drive number into VDP memory. ( I believe this is primarily for boot tracking purposes but may also be for convenience). Without a floppy controller in the system, we had extra VDP RAM up to 0x3fff available for system use. ROS was dumping the filename directly into VDP where my program was located!
The "corruption" is not limited to XB since the ROS routine is executed for all file IO. Had I not been testing file transfers between systems, requiring me to inspect the files for changes, I might have missed out on finding this dependency.
Therefore, for anyone out there using a RAMdisk, it is good practice to keep a floppy controller in the system I do not know if the Myarc hard/floppy controller sets VDP similar to the floppy controllers, that is a test for another day.