This is the application-level interface to the keyboard.  Keystrokes are
processed asynchronously (in the background).  As each keystroke is
received from the keyboard, it is processed by INT 09H and placed into a
circular queue at 40:001e in the BIOS Data Area.

AH  BIOS Service                      Supported by
00H read keyboard input                [PC] [XT] [AT]
01H query keyboard status/preview key  [PC] [XT] [AT]
02H query keyboard shift flags         [PC] [XT] [AT]
03H set typeamatic rate and delay      [PC] [XT] [AT]
04H (reserved)
05H store key data                               [AT]

10H read extended keyboard input                 [AT]
11H query extended keyboard status               [AT]
12H query extended keyboard shift flags          [AT]

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INT 16H: Keyboard Services