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  Service 84H (decimal 132) provides a consistent interface for programs
  that use a joystick or a related input device connected to IBM's Game
  Control Adapter. When you call this service with DX = 00H, the ROM BIOS
  reports the adapter's four digital switch input values in bits 4 through 7
  of register AL. Calling service 84H with DX = 01H instructs the BIOS to
  return the adapter's four resistive input values in registers AX, BX, CX,
  and DX.

  Service 84H is not supported on the IBM PC or in the original PC/XT BIOS
  (dated 11/08/82). Be sure to check the computer's model identification and
  ROM BIOS revision date before you rely on this BIOS service in a program.