Scan-Line Interleave from 3dfx

3dfx

3dfx Interactive was a company that specialized in the manufacturing of 3D graphics processing units and, later, graphics cards. It was a pioneer in the field for several years in the late 1990s until 2000 when it underwent one of the most high-profile demises in the history of the PC industry...

 is a method for linking two (or more) video card

Video card

A video card, Graphics Card, or Graphics adapter is an expansion card which generates output images to a display. Most video cards offer various functions such as accelerated rendering of 3D scenes and 2D graphics, MPEG-2/MPEG-4 decoding, TV output, or the ability to connect multiple monitors...

s or chips together to produce a single output. It is an application of parallel processing

Parallel processing

Parallel processing is the ability to carry out multiple operations or tasks simultaneously. The term is used in the contexts of both human cognition, particularly in the ability of the brain to simultaneously process incoming stimuli, and in parallel computing by machines.-Parallel processing by...

 for computer graphics

Computer graphics

Computer graphics are graphics created using computers and, more generally, the representation and manipulation of image data by a computer with help from specialized software and hardware....

, meant to increase the processing power available for graphics. SLI from 3dfx was introduced in 1998 and used in the Voodoo2

Voodoo2

The Voodoo2 was a set of three graphics processing units on a single chipset, made by 3dfx. It was released in February 1998 as a replacement for the original Voodoo Graphics chipset. The card ran at a chipset clock rate of 90 MHz and used 100 MHz EDO DRAM, and was available for the PCI interface...

 line of graphics accelerators. However, the original Voodoo Graphics card and the VSA-100 were also SLI-capable.

Nvidia Corporation reintroduced the SLI acronym in 2004 (though it now stands for Scalable Link Interface

Scalable Link Interface

Scalable Link Interface is a brand name for a multi-GPU solution developed by NVIDIA for linking two or more video cards together to produce a single output...

) and intends for it to be used in modern computer systems based on the PCI Express

PCI Express

PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...

 bus.

Function

3dfx's SLI design was the first attempt, in the consumer PC market, at combining the rendering power of two video cards. The two 3dfx cards were connected by a small ribbon cable

Ribbon cable

A ribbon cable is a cable with many conducting wires running parallel to each other on the same flat plane. As a result the cable is wide and flat. Its name comes from the resemblance of the cable to a piece of ribbon.Ribbon cables are usually seen for internal peripherals in computers, such as...

inside the PC. This cable shared graphics and synchronization information between the cards. Each 3dfx card rendered alternating horizontal lines of pixels composing a frame.

Criticism

3dfx incorporated the notion of adding an extra video card into its already (relatively) extensive advertising campaigns. Advertisements in various video gaming magazines had contained such quotes as "double the hardware, double the power", or "Twice as fast". Although many believed that adding another expensive card would double frame-rates, this proved not to be the case.

Note: It can now be seen that the original 3DFX SLI was very effective, more so than even current implementations by Nvidia & ATI, capable of achieving near 100% performance increase over a single Voodoo2 card. The reason this could not be observed before as the CPU was the limiting factor.

Aside from this, successfully running the SLI configuration often proved difficult. At the time (as the case with the Voodoo2), some motherboards would not function with three video cards installed (i.e. 2d card, Voodoo2 #1 and Voodoo2 #2). In other cases, there were issues with conflicts as system resources in normal ranges were already accounted for, partly because many features that are today integrated into motherboards (such as the network interface and sound playback facilities) were at that time provided by add-on cards, each requiring additional system resources. Some systems lacked enough open PCI slots to support the setup and additional add-on cards were sometimes sacrificed.

If the technical issues were surmounted, it was further discovered that some applications had problems operating under SLI. Furthermore, those programs that did function sometimes experienced tearing and other display artifacts resulting in a growing number of dissatisfied enthusiasts. Still, a number of fans touted SLI as the future of gaming and as such, SLI became more of a status symbol than a viable system upgrade.

By the time that the setup was cost effective, there were single card solutions that rivaled the theoretical capabilities of the SLI configuration, for lower costs. As a result, SLI received little market presence, although many gamers still consider the 3dfx SLI setup to have been "the" setup to have for hardcore gaming. Although the performance benefit is not always obvious, it did allow higher resolution support of up to 1024x768 compared to 800x600 offered by a single card.