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  Service 13H (decimal 19), allows you to write a string of characters to
  the display screen. Through the four subservices that make up this
  service, you can specify the character attributes individually or as a
  group. You can also move the cursor to the end of the string or leave it
  in place, depending on which subservice you choose.

  The subservice number is placed in AL, the pointer to the string in ES:BP,
  the length of the string in CX, the starting position where the string is
  to be written in DX, and the display page number in BH.

  Subservices 00H (decimal 0) and 01H (decimal 1) write a string of
  characters to the screen using the attribute specified in register BL.
  With subservice 00H, the cursor is not moved from the location specified
  in register DX; with subservice 01H, the cursor is moved to the location
  following the last character in the string.

  Subservices 02H (decimal 2) and 03H (decimal 3) write a string of
  characters and attributes to the screen, writing first the character and
  then the attribute. With subservice 02H, the cursor is not moved from the
  location specified in register DX; with subservice 03H, the cursor is
  moved to the location following the last character in the string.

  Service 13H is available only in the PC/AT, EGA, PS/2s, and later versions
  of the PC/XT ROM BIOS.