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  Service 1BH (decimal 27) is available in all PS/2s as well as with the
  VGA. It returns a great deal of detailed information regarding the
  capabilities of the ROM BIOS as well as the current ROM BIOS and video
  hardware status.

  Service 1BH returns this information in a 64-byte buffer whose address is
  passed in registers ES:DI. In addition to this address, you must also
  specify an "implementation type" value of 0 in register BX. (Presumably
  future IBM video products will recognize implementation type values other
  than 0.)

  The BIOS fills the buffer with information about the current video mode
  (the mode number, character columns and rows, number of colors

  available) as well as about the video hardware configuration (total video
  memory available, display combination code, and so on). See the IBM BIOS
  Interface Technical Reference manual for details on the buffer format.

  In the first 4 bytes of the buffer, the ROM BIOS returns a pointer to a
  table of "static" functionality information. This table lists nearly all
  of the features the ROM BIOS and the video hardware can support: the video
  modes available, support for palette switching, RAM-loadable character
  sets, light-pen support, and many other details.

  When you write a program that runs on a PS/2 or in a system with a VGA
  adapter, service 1BH offers a simple and consistent way for your program
  to determine what the video subsystem's current and potential capabilities
  are. Unfortunately, you can't rely on this service if your program must be
  compatible with non-PS/2 computers. Neither the PC motherboard ROM BIOS
  nor the EGA BIOS supports this service. A program can determine whether
  service 1BH is supported by examining the value returned by this service
  in AL; this value is 1BH if the service is supported.