Code:
MOV   AX, 0     ; AX = 0
MOV   AL, 0     ; AL = 0
MOV   AH, 0     ; AH = 0

MOV   AL, FFh   ; AL = FFh
  ; AX = 00FFh
  ; AH = 00h
;I understand up to here
INC   AX        ; AX = AX + 1
  ; AX = 0100h
  ; AH = 01h
  ; AL = 00h
;but not this. I thought that:
;   since AL (FFh) + 1  = 100
;   and AH (00h) +1 = 01h
;   that AH|AL would be 01|100, but it should be 0100h. What am I missing?