SLI Explained

Much like ATi's Crossfire, NVIDIA SLI is a situation where you add a second similar generation graphics card (or in more GPUs) to the one you already have in your PC and effectively try to double, triple or even quadruple your raw rendering gaming performance. Today for example we place two NVIDIA graphics cards into a SLI compatible mainboard. We bridge them together, install drivers after which most games can take advantage of the extra horsepower we just added into the system.

The idea is not new at all ... if you are familiar with the hardware developments over the past couple of years you'll remember that 3dfx had a very familiar concept with the Voodoo 2 graphics cards series. There are multiple ways to manage two cards rendering one frame; think of Supertiling, it's a popular form of rendering. Alternate frame Rendering, each card will render a frame (even/uneven) or Split Frame rendering, simply one GPU renders the upper or the lower part of the frame. So you see there are many methods where two or more GPUs can be utilized to bring you a substantial gain in performance.

This review will show SLI performance results throughout the benchmark sessions based on two GPUs rendering the game, and later on in the article even three GPUs rending your games.

They look just like identical twins don't they ?

Meet the GeForce 9800 GTX+

So then, with this GTX+ SKU the G92 based graphics processor is no longer based on NVIDIA's 0.65nm silicon, which actually already was a respin chip based on last years architecture from the GeForce 8800 series. NVIDIA made the transition onwards to a much smaller die (chip size), made at a 55nm fabrication process. Why move towards a smaller fabrication process you might ask?

A lower die-size often equals lower core voltages, better energy efficiency and typically better clock speeds. Important to know is that the G92 is based on the same chip that the 8800 GTS 512MB has, which means that the GPU on the 9800 GTX+ also has 128 shader processors.

How many transistors do the NVIDIA GeForce 9800 GTX GPUs have you ask ? No precise data has been given yet, but it's safe to assume roughly 754 million transistors. A question we hear a lot, why is the 9800 GTX 512MB a series 9 product, and the 8800 GTS 512MB (based on the same G92 graphics core), a series 8 product? The answer: I have no idea other then the fact that a Series 9 product sounds better (marketing wise). The G92 based 8800 GTS should probably have been called 9800 GTS or GS as people in the stores right now are really confused.

In summary, the new features of G92+ opposed to the G80: an even smaller 55nm fabrication process, silicon optimizations (compression algorithms), usage of 256-bit memory, and compared to the older GTS models a higher shader processor count at 128 sub-cores.

The core frequency of the regular 9800 GTX runs at 675 MHz, the shader processors at 1675 MHz and the memory at 2200 MHz effectively (70.4 Gbps memory bandwidth); mind you that these are reference speeds.

So purely to counteract the new Radeon 4850 products NVIDIA decided to create another SKU in the market called NVIDIA GeForce 9800 GTX+.

The GeForce 9800 GTX+ thanks to the smaller fab now can run (easily) at 738 MHz, the shader processors at 1836 MHz and the memory at 2200 MHz effectively.

Also the new Series 9 cards are Hybrid Power ready, meaning on future Hybrid mainboards this card can deactivate itself (saving power). One more advantage for the 9800 GTX+ is that you can go three-way SLI with it.

Generally speaking it is a faster clocked NVIDIA GeForce 9800 GTX, and even more importantly the price is dropping pretty significantly towards a suggested retail price of $229 USD. Also the GeForce 9800 GTX will drop towards 199 USD, matching the Radeon HD 4850. You just have to like the competition as it's definitely going to be interesting to purchase a higher specced mid-range card. They'll get you excellent performance for the money you pay.

The card we received from NVIDIA definitely is a notch faster compared to the older GeForce 9800 GTX .