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  Service 01H (decimal 1) controls the form and size of the blinking cursor
  that appears in text modes. The default cursor appears as one or two
  blinking scan lines at the bottom of a character display position. You can
  change the default cursor size by redefining the number of lines that are
  displayed.

  The Color Graphics Adapter (CGA) can display a cursor that has 8 scan
  lines, numbered from 0 at the top to 7 at the bottom. The Monochrome
  Display Adapter (MDA) and the EGA can display a cursor that has 14 scan
  lines, also numbered from the top, from 0 through 13. Both the MCGA and
  the VGA have default text characters that are 16 scan lines high, so the
  maximum size of the text cursor in default PS/2 text modes is 16 scan
  lines. You set the cursor size by specifying the starting and ending scan
  lines. (These are the same as the start and stop parameters of BASIC's
  LOCATE statement.) The start line number is loaded into the CH register
  and the stop line number into the CL register. Default cursor settings are
  CH = 6, CL = 7 for the CGA, CH = 11, CL = 12 for the MDA and EGA, and CH =
  13, CH = 14 for the MCGA and VGA.

  You will notice that the valid scan line numbers occupy only four of the
  bits (bits 0 through 3) placed in these registers. If bit 5 of CH is set
  on by specifying a value of 20H (decimal 32), the cursor will disappear.
  This is one of two techniques that you can use to remove the cursor in the
  text modes. The other technique is to actually move it off the screen, say
  to row 26, column 1. When a graphics mode is set, bit 5 is automatically
  set to keep the cursor from being displayed. Because there is no true
  cursor in the graphics modes, you must simulate one with the solid-block
  character, DFH (decimal 223), or with a change of background attributes.