0:504h Phantom drive flag
Reports the status of a single-drive system when mimicking a two-drive
Examination of this byte will reveal the current status of the single
drive installed on a one drive system. By using this byte, a
programmer can avoid the message 'Insert disk for drive B:' when
working with a single-drive system.
Although the last value, FFh, is undocumented, FFh means the drive
letter has not been determined yet, so using the drive as drive A will
To determine if only one drive is installed, use the equipment list