Hardware Reference
In-Depth Information
Of course, power consumption can vary greatly for different devices such as processors
and video cards, so if you want to be more informed, consult the data sheets or technical
manuals for your specific components. Also, these overall wattage figures do not give the
breakdown covering which of the rails (+3.3V, +5V, or +12V) each device will use. In
some cases, the combination of components used can exceed the available power on a
single rail while still being under budget for the total wattage available from all the rails
combined. That is in fact one reason that people end up purchasing a power supply with a
much higher watt rating than might seem necessary.
Afteryou'veaddedupeverythingIrecommend,multiplythetotalpowerconsumedbyall
your components by 1.5 to estimate the size of power supply required. This allows some
headroomforfutureexpansionandaccountsforthefactthatatcertaintimessomedevices
can draw much more than their nominal power.
If you want an easier way to calculate your estimated power requirements, Asus has a
fairly good power supply wattage calculator that you can use online at the following
URL:
http://support.asus.com/PowerSupplyCalculator/PSCalculator.aspx
. After you fill
in all the fields with the components in the intended system, the calculator gives you an
estimate of the minimum power supply rating you should choose to power the system.
Different types of bus slots can provide different levels of power for cards. Fortunately, it
is rare for any cards other than video cards to use the maximum allowable power.
Table
18.27
shows the maximum power available per slot for different bus types.
Table 18.27 Maximum Available Power per Bus Slot
The biggest cause of power supply overload problems has historically been filling up the
expansion slots (especially with multiple video cards), using high-powered processors,
and adding more drives. Multiple hard drives, optical drives, and floppy drives can create
quiteadrainonthesystempowersupply.Besureyouhaveenough+12Vpowertorunall
the drives you plan to install. Tower systems can be especially problematic because they
have so many drive bays. Just because the case has room for the devices doesn't mean the