I am sorry, I have to disagree with the above. It's possible when laptop is to put into APCI sleep mode s1, the HD still spins but nobody uses sleep mode s1 anymore. Everybody uses mode s3 or s4 (hibernate). Mode s1 still uses too much power, is a very shallow sleep mode, and laptop vendor specially don't go there, they want your snoozing laptop to use as little power as possible, 'les it wakes up with the battery depleted.
I am saying your laptop sleeps with the HD spin down, further I bet a dollar it also parks the head.