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So I'm debating between powering down and sleep mode when toting my macbook around in my backpack. Apple says the HD 'spins down' when in sleep, which obviously means is not spinning. But are the read/write heads completely removed from the platters as in power down or still poised at the last read/write position? If they aren't cleared of the disc, I'm not dragging it around in sleep mode.

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FWIW I've been toting MBPros (all accelerator-enabled models) around in sleep mode for years now with zero issues. Close lid, go. – Ian C. Jul 13 '11 at 13:54
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The heads are parked out of the way. See http://en.wikipedia.org/wiki/Hard_disk_drive#Landing_zones_and_load.2Funload_technology, specifically:

Modern HDDs prevent power interruptions or other malfunctions from landing its heads in the data zone by either physically moving (parking) the heads to a special landing zone on the platters that is not used for data storage, or by physically locking the heads in a suspended (unloaded) position raised off the platters.

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That does lead me to believe it's parked during sleep, and certainly during power-down, but it seems to be talking specifically about emergency situations (power failure, drop detected). "During normal operation heads in HDDs fly above the data recorded on the disks." So is sleep more like 'normal operation' or more like power-down? – Mike Jul 14 '11 at 2:22
When you put it (the macbook) to sleep it'll switch off all non-essential things so as to conserve power, including the hard drives. So they'll be parked. – Olly Hodgson Jul 26 '11 at 15:41
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In a modern hard drive, the heads are suspended above the platters by airflow. If the heads were over the data areas while the platters are not spinning, then they would touch and possibly cause damage. Therefore, hard drives must move the heads away from the data when not spinning.

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