INT 2F - CD-ROM v2.00+ - DRIVE CHECK
AX = 150Bh
CX = drive number (0=A:)
Return: BX = ADADh if MSCDEX.EXE installed
AX = 0000h if drive not supported
nonzero if supported

See also: 2F150D

2F150B - CD-ROM v2.00+ - DRIVE CHECK