INT 2F U - DOS 4+ XMA2EMS.SYS extension internal - INSTALLATION CHECK
AX = 1B00h
Return: AL = FFh if installed
Note:   XMA2EMS.SYS extension is only installed if DOS has page frames to hide.
This extension hooks onto INT 67/AH=58h and returns from that call data
which excludes the physical pages being used by DOS.

See also: 2F1B

2F1B00 - DOS 4+ XMA2EMS.SYS extension internal - INSTALLATION CHECK