registers are a small storage unit that CPU use , example:
mov al, 'A'
mov ah, 'b'
mov ax, 'AB'
in this example we have al, ah and ax registers. and we show that we can store for each one of the and at the same time we can store the two bytes in the ax register.
| Register | H | L |
|---|---|---|
| ax | .. | .. |
in the table we have the ax register and that combine two registers ah and al. (h for high and l for low) each of ah and al can store one byte (8 bits).