Hardware Reference
In-Depth Information
information about DirectX is available from Microsoft at www.microsoft.com/directx .
Note
For benchmarking DirectX 9/10/11 and OpenGL 4.x operations on your graphics/video
hardware, I recommend the UniGine Heaven DX11 benchmark utility, available from
http://unigine.com/products/heaven/ .
Dual-GPU Scene Rendering
In Table 12.16 , I placed the development of dual PCIe graphics card solutions as the ninth generation
of 3D acceleration. The ability to connect two cards to render a single display more quickly isn't
exactly new: The long-defunct 3dfx Voodoo 2 offered an option called scan-line interfacing (SLI)
that pairs two Voodoo 2 cards on the PCI bus, with each card writing half the screen in alternating
lines. With 3dfx's version of SLI, card number one wrote the odd-numbered screen lines (one, three,
five, and so on), whereas card number two wrote the even-numbered screen lines (two, four, six, and
so on). Although effective, use of SLI with Voodoo 2 was an expensive proposition that only a
handful of deep-pocketed gamers took advantage of.
A few companies also experimented with using multiple GPUs on a single card to gain a similar
performance advantage, but these cards never became popular. However, the idea of doubling
graphics performance via multiple video cards has proven too good to abandon entirely, even after
3dfx went out of business.
NVIDIA SLI
When NVIDIA bought what was left of 3dfx, it inherited the SLI trademark and, in mid-2004,
reintroduced the concept of using two cards to render a screen under the same acronym. However,
NVIDIA's version of SLI has a different meaning and much more intelligence behind it.
NVIDIA uses the term SLI to refer to scalable link interface. The scaling refers to load-balancing,
which adjusts how much of the work each card performs to render a particular scene, depending on
how complex the scene is. To enable SLI, you need the following components:
• A PCIe motherboard with an SLI-compatible chipset and two PCIe video slots designed for SLI
operation
• Two NVIDIA-based video cards with SLI support
Note
Originally, you needed to use two identical cards for NVIDIA SLI. With the introduction of
NVIDIA ForceWare v81.85 and higher driver versions, this is no longer necessary. Just as
with the AMD CrossFire and CrossFireX multi-GPU solution, the cards need to be from the
same GPU family, but they don't need to be from the same manufacturer. You can obtain
updated drivers from your video card maker or from the NVIDIA website ( www.nvidia.com ) .
In most cases, a special bridge device known as a multipurpose I/O (MIO) connects the cards.
The MIO is supplied with SLI-compatible motherboards, but some SLI-compatible cards don't
use it.
To learn more about SLI and for a list of SLI-compatible GPUs and nForce motherboard
chipsets, visit NVIDIA's GeForce SLI website
 
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