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The truth behind 10 energy efficiency myths

Which power saving techniques actually work?

Before you start implement energy efficient methods, it's worth thinking about whether they actually work. We've looked at 10 of the most popular energy efficiency myths and investigated whether they are true or not.

6. A laptop doesn't use any power when it's suspended or sleeping. USB devices charge from the laptop's AC adaptor

Fact: Sleep (in Vista) or Hibernate mode (in XP) saves the state of the system to RAM and then maintains the RAM image even though the rest of the system is powered down. Suspend saves the state of the system to hard disk, which reduces the boot time greatly and allows the system to be shut down. Sleeping continues to draw a small amount of power, between 1W and 3W, even though the system appears to be inactive. By comparison, Suspend draws less than 1W. Even over the course of a year, this difference is probably negligible.

Powering a laptop off doesn't necessarily reduce power usage to zero. This is easily confirmed by touching the power supply of a laptop that has been powered off for a while; it'll still be warm. Unless you unplug the power supply, it still burns energy.

7. Laptop batteries just wear out. There's not much you can do to make them last longer

Fact: Many laptops with nickel-cadmium batteries come with a battery-reconditioning utility that drains the battery fully, then brings it back to a full charge. Laptops with lithium-ion batteries aren't afflicted with the same memory problem as those powered by NiCad batteries. However, unlike NiCad batteries, lithium batteries prefer to be only partially discharged: running them all the way down will shorten their life span.

The calibration utility for lithium batteries actually just recalibrates the capacity measurement to reflect the loss of capacity over time; it doesn't affect actual battery life. Battery life for either type of battery can be prolonged greatly by removing the battery when the unit is plugged into AC power. This approach is recommended if your laptop supports it and power outages are infrequent in your area.

8. Flash solid-state drives (SSDs) reduce the amount of power consumed by a laptop

Fact: You may or may not experience a reduction in power consumption if your system is equipped with an SSD. It will vary greatly depending on the application. Typical office applications that don't constantly access the hard drive will show very little additional battery life with an SSD installed. Software that streams data from the drive constantly, such as video applications, will show greatly increased battery life. Other power savers such as LED backlighting can save more energy in typical applications.

NEXT PAGE: Will going to DC power save energy?

  1. We investigate which power saving techniques actually work
  2. Is it better to pack a server with all it can hold rather than use multiple small servers? We find out
  3. A laptop doesn't use any power when it's suspended or sleeping
  4. Will going to DC power save energy?

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