Hardware Reference
In-Depth Information
To calculate the cost of each device you need to know the cost per kilowatt hour that your utility company charges
you, and plug it into the formula:
Total_cost = (Wattage_of_device × hours_used × kilowatt_hour_charge) ÷ 1000
To reduce consumption costs, you can do several small things for both the computer and the other home
hardware connected to it.
First, switch it off. This applies primarily to consumer electronics such as monitors and TVs, whose power
consumption in standby is almost as high as it is in normal mode, and it is sometimes said that 16 percent of your
annual energy bill is spent on appliances in standby mode. Various products on the market detect standby mode
either by monitoring the drop in power usage or by catching the IR signal to switch off the TV and consequently
isolate all power to the device. In this mode it is, however, impossible to switch it back on automatically. You can
manage this automatically using X10 or C-Bus. Remember that when switching the device back on, you might also
need to send an IR signal if the appliance returns to a standby mode, instead of switching on fully.
Second, stop hard drives spinning. This reduces their consumption from 7W to around 1W, depending on device.
You can achieve this with the
hdparm
tool by configuring it like this:
# /etc/hdparm.conf
/dev/sda {
spindown_time = 60 # this means 5 minutes, since each spindown unit is 5 seconds
}
N
This is reported to work only when the BIOS supports AHCI. In all other cases SATA drives should be controlled
with the
sg3-utils
package.
Note
From a longevity point of view, however, hard disks should not be continually spun up and then down since the
ball bearings will grind more and eventually wear out. Furthermore, the cost of getting them to spin back up is very
high, so you really need to have kept them spun down for around 20 minutes to make the savings worthwhile.
Switch into standby, suspend to RAM, or hibernate to disk mode, each saving progressively more power than the
previous one. The Advanced Power Management (APM) daemon and tools handle the process itself, while the
sleepd
daemon can be to used to trigger the APM tools automatically upon certain conditions, such as lack of activity or input.
Use alternative components. With the green lobby influencing most companies, you can buy more power-efficient
devices than ever before. Better power supplies
6
can provide efficiencies in excess of 80 percent on moderate loads
(90W), less powerful graphics cards use less power generally speaking (and often don't need fans), LCDs monitors are
more efficient than CRTs, and the power usage in CPUs can vary wildly, so consider replacing them.
Unplug any unused devices, such as the CD drive used once for installation (but never again), USB units, and so
on. This can be extended by using external hard disks throughout your system (with the exception of the boot device),
which can be powered down via X10 after unmounting.
Make use of more solid-state discs and/or laptop hardware where possible. Both are intended to work from
batteries and therefore have more suitable CPUs and hardware inside them. For the primary control server, these are
perfectly adequate.
Use virtual machines (running on VMware, for example) instead of using a completely separate machine. This
can offer real benefits when a particular device requires a specific version or operating system. The extra power used
in processing the virtual is far behind that of a physical machine.
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