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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.

3. The power rating (in Watts) of a CPU is a simple measurement of the system's efficiency

Fact: Efficiency is measured in percentage of power converted, which can range from 50 to 90 percent or more. The AC power not converted to DC is lost as heat, which increases the cooling burden of the system, adding even more to the overall energy loss. Unfortunately, it's often difficult to tell the efficiency of a power supply, and many manufacturers don't publish the number. You can either look for systems with published efficiency numbers or measure the actual power draw of various systems at idle and full load, then make your decisions based on that.

4. It's better to pack one big server with all the RAM, CPUs, and peripherals it can hold rather than to use multiple smaller servers

Fact: This is only true if the big server is fully utilised, which can be dangerous with critical applications. Multiple smaller servers can be powered off or put in suspend mode when not in use, and they are safer from a redundancy point of view.

Also, populating a system with as many CPU cores and as much RAM as it will hold will result in a system that uses substantially more power than a base configuration of one dual-core CPU and a modest amount of RAM. Tailoring the server configuration to the software you'll be running can save energy without resorting to extreme measures.

5. LCD monitors use a trivial amount of power, so you might as well leave them on. Their colors and backlight brightness improve with warm-up time

Fact: The average 17in LCD monitor consumes 35W of electricity. Adding together the hundreds of LCDs in an enterprise, the power used may not be that trivial. Energy Star LCD monitors will power down to sleep mode if the PCs' power management software is set up to tell them to. This saves energy and cash - between £6 and £21 per year, according to Energy Star - though not as much as simply turning the monitor off when it isn't in use. Even with the monitor turned off, an LCD's power supply will use between 1 and 3W of power. The only way to get it to zero is to unplug the power supply.

As for warm-up times, they are much shorter than they used to be. LCDs with LED backlighting rather than fluorescent don't need any warm-up time at all.

NEXT PAGE: A laptop doesn't use any power when it's suspended or sleeping

  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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