10 power-saving myths debunked

Is powering a server off and on bad for the system? We disprove this legend and others

Myth No. 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 utilized, 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.

Myth No. 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 17-inch LCD monitor consumes 35 watts 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 US$10 and $40 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 3 watts 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.

Myth No. 6: A notebook doesn't use any power when it's suspended or sleeping. USB devices charge from the notebook's AC adapter.

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 1 and 3 watts, even though the system appears to be inactive. By comparison, Suspend draws less than 1 watt. 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.

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Logan G. Harbaugh

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