[AT]
Expects: AH    15H
DL    drive: 00H thru 03H = diskette drive
80H or 81H   = hard disk
                                                                  
Returns: AH    00H = not installed
01H = diskette drive: can't detect disk change
02H = diskette drive: CAN detect disk change
03H = it's a hard disk
else= BIOS disk error code if CF is set to CY
                                                                  
Info: This checks to see if a hard drive or diskette drive is
installed.

For diskette drives, this also finds if the drive is capable of
detecting change-line status (that is, will it be able to sense
when the drive door has been opened).

Notes:   On diskette drives which detect change-line status, you can use
INT 13H 16H to learn if the disk has been swapped.

See Also: DOS fn 440dH 68H (IOCTL sense media type)
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INT 13H 15H: Get Diskette Type or Check Hard Drive Installed