Introduction

NVIDIA SLI

3dfx's Voodoo2 graphics chipset was wildly popular with gamers when it was originally introduced in 1998. Thanks to increased clock frequencies and other improvements, the Voodoo2 offered significantly better performance than its predecessor, Voodoo Graphics, which was the fastest graphics card at the time. Voodoo2 was also the first consumer-level graphics chipset capable of multi-texturing (the ability to render multiple textures per pixel in one pass), thanks to the addition of a second TexelFX2 chip. The end result was a product that delivered over twice the performance of anything else on the market with impressive image quality for its time, and, thanks to 3dfx’s Glide API, excellent compatibility with a wide range of games and applications.

The feature that really caught everyone’s eye with Voodoo2 however was its support for SLI, scan-line interleaving. By combining two Voodoo2 graphics cards together, performance nearly doubled, and a new resolution was opened up: 1024x768.

SLI worked by splitting the workload in half, one Voodoo2 card rendered the even lines on the screen, while the second card rendered the odd lines. The cards were linked by a pass-through cable with the only requirement being that the cards were of the same configuration and manufacturer.

Critics touted SLI as being impractical. Voodoo2 boards were initially tough to find and priced at $300, well out of the budget of most consumers. Also keep in mind that Voodoo2 was a 3D-only solution, after forking over $600 for an SLI config, you still needed a third graphics card to handle 2D duties, this created a new super high-end segment of the 3D graphics market, replacing the $300 price point that was established with Voodoo Graphics and Voodoo2.

PCI Express 6800 Ultra card

Dual DVI on the back plate

Despite all of this, the letters S-L-I really took off with gamers – even if you couldn’t afford it, you still knew what it was and one day hoped to pair your current Voodoo2 card with its twin. Hardcore gamers and hardware enthusiasts responded passionately to SLI, according to estimates, 30% of consumers picked up a second Voodoo2 card.

AGP appears

While 3dfx was cashing in on SLI, the rest of the industry was well into the transition from PCI to the faster AGP interface. Since none of the early AGP specifications have provided for dual graphics configurations, graphics manufacturers have had to come up with some pretty clever solutions to provide this capability.

Metabyte was first with their “Stepsister” technology, officially dubbed PGC (Parallel Graphics Configuration). In fact, we previewed this technology back in February 1999. PGC worked by splitting the workload into two pieces, the AGP card handled the top of the scene while the PCI card rendered the bottom, but it wasn’t a 50-50 split; since the AGP card offered a little more bandwidth, it could handle 60% or 70% of the work, while the PCI card took care of the rest. Unfortunately for Metabyte however, it took them awhile to get the technology perfected. By the time it was ready for the public, next-generation cards were released for the AGP interface only, no one was interested in a high-end PCI graphics card. PGC was also never entirely effective at load-balancing: the top segment of the screen isn’t always as complex as the lower half. PGC never truly addressed this. The technology was eventually acquired by Alienware and faded into obscurity.