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Micro-Stuttering And GPU Scaling In CrossFire And SLI

Micro-Stuttering, Multi-Card Scaling, And More!

Single GPU or multi-card setup? That's a question we face every time we start a System Builder Marathon series or evaluate the worth of a flagship GPU. 

Do you want a just one high-strung racehorse or a pair, trio, or quartet of draft horses? Can a team of inexpensive cards perform the work of an pricier one and still come in at a lower cumulative cost?

Welcome to Groundhog Day. Due to recurring forum questions and direct requests by our readers, we decided that it's time to go beyond the usual performance-oriented benchmarks of CrossFire- and SLI-based systems, and shed some light on the underlying principles. Frame rates in and of themselves do not necessarily translate into a high-quality experience.

Yes, we're going to tackle the issue of micro-stuttering, which seems to keep so many sensitive eyes from investing in multiple cards running in concert. We'll also look at the scaling of two, three, and four GPUs. Where is the benefit? And at what point is actual added value really realized, or is churning out high (but ultimately useless) frame rates a self-defeating exercise? As we're sure you can imagine, at some point, the pursuit of performance can become a money pit and a power hog. At the same time, we've seen multi-card setups yield incredible value.

What Has Changed?

When it comes to measuring the scaling of mid-range cards, we run into a little problem. AMD and Nvidia try to limit the amount of expansion you can achieve with those less expensive boards by only exposing one bridge connector, limiting us to two-card configurations. Conversely, cards with two bridge connectors (enabling three- and four-way arrangements) are only found at the high end of the price spectrum. 

For most folks, the prospect of anything beyond two high-end cards simply gets too expensive. Enter PowerColor's Radeon HD 6870 X2. It features two mid-range GPUs on a single PCB, consequently allowing us to set up and test four-way CrossFire with mid-range chips. As a result, we have the opportunity to compare a typical mid-range card like the Radeon HD 6870 (a $180 card) in a two-way setup to a single Radeon HD 6870 X2, and then add a three-way setup (Radeon HD 6870 X2 + 6870) and the four-way results.

Additionally, we compare those three configurations to a number of current cards, right up to the GeForce GTX 590, in a comprehensive set of benchmarks. Our goal is to evaluate performance, assess the seriousness of micro-stuttering, and finally rank the cards based on raw performance and their price/performance ratios. Are we due for a surprise? Nothing can be ruled out; we invite you to read on!