Int 21 Fn 4321  - Q87, Q387 - Installation Check                           [u]

   AX = 4321h
   BX = 0000h
   EAX = 87654321h (entire EAX value is required, not just AX)

Return: EAX = 12345678h if installed
Program: Q387 (renamed to Q87 as of v3.7) is a math coprocessor emulator from
     Quickware

Note:  this function is available only in virtual-86 mode in older versions;
     newer versions also provide it in MS Windows 16- and 32-bit protected
     mode

See Also: AX=4321h/BX=0001h,AX=4321h/BX=0002h,INT 67/AX=4321h