[assembly] How do AX, AH, AL map onto EAX?

AX is the 16 lower bits of EAX. AH is the 8 high bits of AX (i.e. the bits 8-15 of EAX) and AL is the least significant byte (bits 0-7) of EAX as well as AX.

Example (Hexadecimal digits):

EAX: 12 34 56 78
AX: 56 78
AH: 56
AL: 78