Flash memory is often touted as a possible replacement for hard drives in portable computing devices. It certainly has a dominant position in the personal music player market. One of the main reasons cited for this, apart from physical space savings, is the lower power requirements of flash compared with hard disks. A reduction in power drain for a device can also reduce the overall weight of the product because the battery can be made smaller and lighter. This raises the question of just how much power, and thus battery is saved when using flash instead of a hard drive. Hard drives will typically have 4 states of power drain, those being startup, active, idle and standby. The startup phase is when a drive starts spinning when turned on or coming up from standby mode. This is typically the highest level of power drain. Active is when the disk is up to normal rotational speed and is being read from or written to. Idle mode is when the disk is spinning but is not being written or read. Lastly, standby mode is when the disk is not spinning at all. Standby is the lowest level of power drain.
To give a perspective on just how much less power flash memory uses compared with hard drives here are 4 charts featuring the commonly available form factors of hard disks and their typical power drain compared with flash memory performing a similar function.
Startup
uses the most power for hard disks because of the extra energy
need the accelerate the spinning platters to operational speed.
Startup time for a disk usually takes about 3 seconds. Because
flash has no mechanical parts, it does not have any peak energy
requirements when powering up. It is also ready to operate in a
few thousandths of a second.
When reading or writing, flash uses no more that 100 milliwatts. Much more efficient than even the tiniest hard disk.
Idle mode is not very relevant to flash as it doesn't have to use energy to keep a disks spinning. There is a small amount of power used to keep the controller running but this is negligible compared to the powered used to keep a disk spinning.
Standby mode is where hard drives use the least power. They still manage to use more than a lot more than flash. In fact they use at least as much in standby mode as flash does actively reading.
Data for the charts came from Toshiba, Seagate and Wikipedia.