Apple introduced its version, called Fusion Drive, that tiers storage on flash memory or a HDD depending upon frequency of use, but appearing to the user as a single storage device.

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Depending upon how loose you want to be with your statistics, the frequency is either staying the same (conservative stats) or actually in decline (loosey-goosey stats).

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Continuing to reduce the costs of on-line storage will require the management of stored content to optimize availability depending upon frequency of use and use of commodity storage and other data center equipment.

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