INT 2fH 150dH: Query CD-ROM Drive Letters

                                                         Compatibility: 6.0+ 
 Expects: AX    150dH
          ES:BX address of buffer to receive drive letters
 Returns: ES:BX buffer contains data
    Info: Obtains a list of DOS logical drive letters that are mapped to

    ES:BX on entry, this buffer must be at least as long, in bytes, as the
          value obtained by a previous call to INT 2fH 1500H (count

          On return, the buffer contains a series of one-byte values
          identifying the CD-ROM drives, where 0=A, 1=B, 2=C, etc.

          For instance, if there are two CD-ROM drives, and ES:[BX+0]=0cH
          and ES:[BX+1]=12H, then drives M and S are CD-ROMs (i.e.,
          'A'+0cH='M' and 'A'+12H='S').

See Also: INT 2fH: Multiplex Interrupt
          DOS Functions