Percival P. Cassidy wrote:

http://www.tomshardware.com/news/hdd...ate,36132.html

Defragmenters will have to adopt new algorithms so they position
sequential data not in successive clusters within the same track on the
same platter but jigsawing the data across multiple platters. So one
head can read one cluster of data while a head on the other arm can be
reading the next logically sequential cluster of data in building up the
data stream.

So they split the arm into 2 arms to increase access speed. Still
limited to just 2 heads at a time. Maybe they'll eventually use
separate arms for each platter. I suspect the noise level will go up.
Instead of one arm making chunking noise, now there will be 2, then 4,
then 8, then 16. Wonder how much more the multi-arm drives will vibrate
which will require more insulating to dampen the vibration transmitted
to the cage and then to the case.