The most compelling reason to install multiple GPUs is to drive multiple high-resolution displays. The secret's out that "multi-mon" is the single best way to improve your productivity. Anyone who's gone to two displays (or three — or more!) will tell you they could never go back to one. And more graphics cards can display more pixels across more monitors.
Which Graphics Card Works for You?
That said, you don't necessarily need to populate two cards to run two monitors, so pay attention to the cards you're selecting. NVIDIA's Quadro with nView and Mosaic technology can support two displays across most of the product line. A single high-end AMD FirePro V7900, with its Eyefinity technology, can handle four on its own, thank you very much. As such, if your performance demands have you buying midrange or high-end cards, you might get all the screen real estate you want with one card. But if you're much hungrier for pixels and screens than you are for polygons per second, you might consider two less-expensive, dual-monitor cards.
On top of multi-monitor support, you can use that extra slot to turn your workstation into a supercomputer. An exaggeration? Not to some. General-purpose computing on GPUs (GPGPU) technology is still evolving, but many of the applications that show the most promise are the ones of most interest to engineers and other CAD users: applications such as computational fluid
dynamics (CFD) and finite-element analysis (FEA). Simulation software developers such as ANSYS and Abaqus are porting code to harness GPUs to deliver big speed-ups — in many cases tenfold or even 100- fold increases — over CPU-only computation.
High-end graphics cards usually require more power than the 75 watts supplied by the typical x16 PCI Express interface. Workstation OEMs accommodate their extra needs via auxiliary power cables drawn from the supply. Some high-end and virtually all ultra high-end graphics cards are dual-slot thickness. They insert into one PCI Express x16 connector, but their thickness means an
adjacent x16 slot may be blocked and rendered useless.
Make the Right Choice
When purchasing a workstation online, the OEM's product configurator should let you know if the chosen card or cards will mate to the chosen system, with respect to power supplies and connectors, the number of available PCI Express x16 slots, and whether a dual-slot card has sufficient clearance. For example, when outfitting graphics on a smaller chassis that can't accommodate two dual-slot cards, chances are the OEM will only offer the option of two entry-level or two mid-range cards, both of which are single slot width.
For that matter, if you're perusing the latest flavor of entry level workstation, full-length cards may not have clearance lengthwise. Again, the online configurator should ensure compatibility, so you shouldn't have to worry about these issues.