
Since there is no BIOS support for ST-506 interface hard disks in an XT,
that support must come from a BIOS extension ROM on the (MFM/RLL) hard disk
controller. Usually the controller has a ROM-based low level format
program (a common jump address is C800:0005 ... you can type G=C800:5 from
debug to see) and a small table of drive geometries it "knows" about.
Sometimes these are selectable using jumpers on the card, sometimes you
can enter them manually in the LLF menu. Failing that, you must use a
third-party HD prep program like SpeedStor, Disk Manager, or the like.

IDE drives come formatted already, and since the is controller part of the
drive mechanism itself, concerns about geometry are irrelevant. Plug
it in and go to FDISK.
