0:41Ch                   Keyboard Buffer Tail Pointer

 Length: 2 bytes

    This word points to the location in the keyboard buffer at which the
    next character typed will be placed. After a character is placed in
    the keyboard at this location, the tail pointer is incremented and
    adjusted if it needs to wrap to the beginning of the keyboard buffer.
    If the tail pointer is equal to the head pointer (0:41Ah), the buffer
    is empty.