Page 90 -

C C h a p t e r 3 : h a p t e r 3 : M i n i m i z i n g P o w e r U s a g e i n i m i z i n g P o w e r U s a g e 61 61
M

NOTE Screensavers seem like they should save power, but they don’t—they just save the screen
from burn-in. After all, something is still being displayed on your screen. That said, not all
screensavers are created equal. If you must rely on a screensaver rather than powering down the
monitor, use a stock Windows screensaver, such as Marquee or Stars. These use less power than
custom-made screensavers. Also, have you ever noticed how your CPU (and the fans) goes into
hyperdrive when trying to render a complicated, animated screensaver?

Power Supplies
If you have a say in the components that go into your computers or other devices, use those
that conform to the 80 Plus standard. This requires power supplies in computers and
servers to be 80 percent or greater energy efficient at 20 percent, 50 percent, and 100 percent
of the rated load. PART II
The EPA finalized updated performance requirements for computers and servers that
include the more efficient 80 Plus standards. These requirements took effect July 2007.

Wireless Devices
Radios consume power for both transmitting and receiving. Most laptop adapters use their
radios, even if they’re not connected to an access point (AP). Let’s talk about how you can
minimize excessive power output from these devices.

WiFi
APs announce their presence at regular intervals by sending a beacon packet. The default
interval for most APs is set to 100 milliseconds. The impact of the beacon interval is most
noticeable when it’s trying to find a network to associate with. This is shown in Figure 3-8.
Association requires a WiFi radio to tune to each channel and listen for the AP to
broadcast a beacon. The longer between the intervals, the longer the radio must wait on
each channel.
In addition to the radio overhead, the downside of a lot of broadcast beacon packets is
that with some wireless adapters, the computer must come out of power-saving idle states
to process the packets. For laptops that are close to the AP, you may be able to save a little
bit of power by going into the administrative page of the AP and increasing the beacon
interval.

FIGURE 3-8 The access point is
APs regularly constantly transmitting
transmit beacon beacon packets so the
packets so that laptops know it is
wireless clients available.
can find them.

Access point Laptops