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iPod Dies at Altitude. I've been using my 15gb iPod to supply music in my unpressurized airplane. Today I decided to fly high, returning to the S.F. Bay Area from Las Vegas. At FL190 (~19,000'), my iPod got weird. I could feel the disk seeking, and the display kept resetting. Upon landing, it started up and worked fine. I checked the iPosd web site and saw that the unit's max altitude is 10,000' (3,000 meters). I wonder what's pressure sensitive. Sealed disk drive?
Update from Stephen Pierce, a fellow pilot: My job is dealing with large numbers of spinning metal (disk drives). Disk drives are *not* sealed containers. They have special filters and will equalize pressure. When you take a hard drive up high, the inside pressure will reduce.
Hard drives work by levitating a head a very small distance from the media; unlike floppy or tape, where the media actually touches the head. The distance between the rotating media and the head is regulated using a very small wing on the head. The head literally 'flys' above the media.
When the pressure inside the drive is reduced, the wing will need a higher angle of attack, until finally the wing stalls, and the head impacts the media. The term in the industry for this behavior is called a 'head crash'. Very apropos, no?
In old hard drives, repeated head crashes will cause a data block to be
unreadable. Modern drives compensate by relocating data from a bad block to special hidden blocks preallocated for that purpose. So, I'm not surprised that your ipod worked after a head crash; the data was reallocated at some point when the drive started working again.
Also, a head crash will occur when you stop spinning the disk drive. In
older media, this would result in a 'soft crash', usually without damage to data. Older computer users will remember programs that would 'park' your hard drive for shipment. Parking heads moves them to a position where the head will land on a 'soft', non-media spot. All modern drives 'auto-park' heads using the rotational inertia once the power is cut.
Posted Friday, October 31, 2003 3:24:52 PM 
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