Int 16 Fn FFA5  - PC-cache V6+ - Installation Check                        [c]

   AX = FFA5h
   CX = 1111h

Return: CH = 00h if installed
       ES:DI -> internal data (see below)
       CL = cache state
       01h enabled
       02h disabled

See Also: INT 13/AH=27h,INT 13/AH=A0h,INT 21/AH=2Bh/CX=4358h

Format of internal data:
Offset Size    Description
-1Ch 20 BYTEs  cached drive list, one byte per drive A: to T:
       each byte is either blank (20h) or drive letter (41h-54h)
 -8    BYTE    ???
 -7    WORD    number of physical transfers (scaled down to 0000h-7FFFh)
 -5    WORD    number of saved transfers (scaled down to 0000h-7FFFh)
 -3   3 BYTEs  ???