Compatibility: All
Expects: AH    09H
AL    character to write (see ASCII Table)
Note: Graphics chars > 127 are defined in INT 1fH table.
BH    video page number (0-based)
BL    text modes:     video attribute for character
graphics modes: color number
CX    repeat count
                                                                  
Returns: (none)
                                                                  
Info: This writes a character and attribute to the current cursor
location.

This is too slow for most apps.  See Video Memory Layouts.

CX To write just one character, set CX=1.

You may use the fn to write a series of the same character--for
instance, to fill an entire screen line with blanks--by setting
CX to a repeat count.

Notes: This does not update the cursor position.  Use INT 10H 0eH to
write a character and advance the cursor.

Use INT 10H 0aH to write a character without modifying the video
attributes of the affected screen positions.

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INT 10H 09H: Write Character/Attribute to Cursor Location