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  Function 66H (decimal 102), also introduced with DOS version 3.3, consists
  of two subfunctions that provide support for code page switching within a
  program. Call this function with a subfunction number (01H or 02H) in AL.

  Subfunction 01H. This subfunction returns the number of the active code
  page in BX. It also reports (in DX) the number of the default code page
  used when the system is first booted.

  Subfunction 02H. Call this subfunction with a new code page number in BX.
  DOS copies the new code page information from the COUNTRY.SYS file and
  uses it to update all devices configured for code page switching. For this
  subfunction to operate successfully, you must include the appropriate
  DEVICE and COUNTRY commands in your CONFIG.SYS file and also execute the
  MODE CP PREPARE and NLSFUNC commands. (See your DOS reference manual for
  details.)