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How Can Battery Runtime Be Shorter?

... In the case of sequential reading or writing, hard drives will not require much more than the idle power, as there is no energy-intensive acceleration and deceleration of the actuator.

Flash SSDs Only Know Two Power States

In contrast, flash SSDs only seem to know two states: active or idle. We don’t have specific information on this, but we received confirmation from two vendors that many flash devices don’t feature power saving mechanisms yet. On the one hand, the entire industry is looking to improve MLC flash to enable larger flash SSDs at sufficient performance levels. On the other hand, wear leveling algorithms are more important than power saving features, as durability may be an issue with SSD drives.

So while conventional hard drives may operate at relatively low power when little movement is required — such as during sequential read access — flash based drives do not. They will draw their maximum power level constantly when in use, and as a consequence, simply spend more total time drawing maximum power than conventional drives.