Hardware Reference
In-Depth Information
least 192 and 288 watts, respectively, using standard terminals, and even more using the
HCS or Plus HCS terminals.
Thesetwoauxiliarypowerconnectorsaresometimescalled
PCI Express Graphics (PEG)
,
Scalable Link Interface (SLI)
, or
CrossFire
power connectors because they are used by
high-end PCI Express boards with SLI or CrossFire capabilities. SLI and CrossFire are
NVIDIA and AMD's methods of using two video cards in unison, with each one drawing
half of the screen for twice the performance. Each card can draw hundreds of watts, with
many of the high-end cards using two or three auxiliary power connectors. This means
that most power supplies that are rated as SLI- or CrossFire-ready include at least two or
moreofthe6/8-pinPCIExpressgraphics powerconnectors. Usingtwovideocardsdraw-
ing 300 watts each means that even if you have a 750-watt power supply, you will have
only 150 watts of power left to run the motherboard, processor, and all the disk drives.
With high-powered processors drawing 130 watts or more, this may not be enough. For
this reason, systems using two or more high-end video cards require the highest-output
supplies available, and some of the current ones are capable of putting out up to 1,000
watts (1 kilowatt) or more.
Note
NVIDIA has trademarked the term
SLI
as meaning
scalable link interface
, but its primary
competitor, AMD, uses similar dual-graphics card technology called CrossFire to achieve
comparable performance improvements.
If your existing power supply doesn't feature PCI Express auxiliary power connectors,
you can use Y-adapters to convert multiple peripheral power connectors (normally used
for drives) into a single 6-pin or 8-pin PCI Express auxiliary power connector. Note,
however, that these adapters will not help if the power supply is not capable of supplying
the total power actually required.
Power Supply Specifications
Power supplies have several specifications that define their input and output capabilities
as well as their operational characteristics. This section defines and examines most of the
common specifications related to power supplies.
Power Supply Loading
PC power supplies are of a
switching
rather than a
linear
design. The switching type of
design uses a high-speed oscillator circuit to convert the higher wall-socket AC voltage
to the much lower DC voltage used to power the PC and PC components. Switching-type
power supplies are noted for being efficient in size, weight, and energy compared to the
