Inside the graphics core
So here we meet again. Welcome .. let's chat a little about the G71. What's G71 you ask ? This is the codename of the chip from it's development stages. Most of you figured we'd see a 32 pixel pipeline product today. And yeah .. I was hoping it also but perhaps we have been a little to ambitious in our thinking. We'll likely have to wait on the G80 silicon for that. None the less this product is screamingly fast though.
So in essence there are three factors changed on the G71 versus G70. A smaller fabrication process at 90nm, a higher core clockspeed and of course faster memory bandwidth. That G71 chip is different though, as the transistor count went down. The 7800 GTX for example has 304 million transistors where the new 7900 GTX has 278 Million so there are differences for sure. Now we haven't received the whitepapers just yet and I unfortunately had to miss out on an NVIDIA product briefing, but word is that the new chip is based on 48 ALUs. The G71 has been manufactured at NVIDIA's latest 90nm fabrication process. Smaller fabrication processes of course offer several advantages. You could push more transistors on the GPU as you have more space to work with, but another nice advantage is a smaller chip design. That means you need to cram in less voltage into the silicon and that saves on heat. Less heat means higher clockspeeds and that's why today's product is clock roughly 100 MHz faster then it's predecessor the 7800 GTX 512MB. Did you know that the 256MB version is clocked at 430 MHz ? You can smell the performance there huh ? Really it's not all about clock for clock performance .. but it can surely help :)
Since we are on the topic of the graphics core, inside it there are precisely eight vertex units active. Also the number of pixel pipelines are identical to the 7800 GTX, there are twenty-four of them. Let me enlighten briefly what happens in the pixel pipeline for you to understand its importance. Each pixel that is rendered on your screen goes through a pipe where it'll receive its complex color/effect etc. Each time that pixel is altered it'll pass through the pixel pipeline, one pass is one clock cycle.

The 7800 GTX throughout the Series 7800+ line has had eight ROPs. ROP is short for Raster OPeration and a portion of a pipeline, responsible for AA, Blending and Z-Buffer compression. Simply stated a ROP is basically the output engine of a pixel shader pipeline. The pipeline is scalable, each pipe is available at any time in sets of 4, which we call quads.
Of course next to the GPU the most important thing is it's memory to work in. We call this the framebuffer, and the faster it is the higher your memory bandwidth to work in will be. Suffice to say is that the 7900 GTX 512MB is armed with the latest and fastest memory available ... the eVGA version comes with a clock of 1760 MHz .. and that's a lot of bandwidth for sure.
Please focus on the chart below where I cite the more important specs.
|
NVIDIA GeForce 6 & 7 Product Lineup Specifications |
|
Product Name |
# pixel processors |
# vertex processors |
Bus width |
Memory Type/Amount |
GPU Speed |
RAM Speed |
| GeForce 7900 GTX |
24 |
8 |
256-bit |
GDDR3/512MB |
650-700MHz |
1600 MHz |
| GeForce 7900 GT |
24 |
8 |
256-bit |
GDDR3/256MB |
450MHz |
1320 MHz |
| GeForce 7800 GTX |
24 |
8 |
256-bit |
GDDR3/512MB |
560MHz |
1600 MHz |
| GeForce 7800 GTX |
24 |
8 |
256-bit |
GDDR3/256MB |
430MHz |
1200MHz |
| GeForce 7800 GT |
20 |
7 |
256-bit |
GDDR3/256MB |
400MHz |
1000MHz |
| GeForce 7800 GS |
16 |
6 |
256-bit |
GDDR3/256MB |
375MHz |
1200MHz |
| GeForce 7600 GT |
12 |
5 |
128-bit |
GDDR3/256MB |
560MHz |
1400MHz |
|
GeForce 6800 Ultra ** |
16 |
6 |
256-bit |
GDDR3/256MB |
400MHz |
1100MHz |
|
GeForce 6800 GT |
16 |
6 |
256-bit |
GDDR3/256MB |
350MHz |
1000MHz |
| GeForce 6800 GS PCX |
12 |
5 |
256-bit |
GDDR3/128/256MB |
425MHz |
1000MHz |
| GeForce 6800 GS AGP |
12 |
5 |
256-bit |
GDDR3/128/256MB |
350MHz |
1000MHz |
|
GeForce 6800 |
12 |
5 |
256-bit |
GDDR/128MB |
325MHz |
700MHz |
|
GeForce 6800 LE |
8 |
4 |
256-bit |
GDDR/128MB |
320MHz |
700MHz |
| GeForce 6600 GT |
8 |
3 |
128-bit |
GDDR3/128/256MB |
500MHz |
1000MHz |
| GeForce 6600 |
8 |
3 |
128-bit |
GDDR/128MB |
300MHz |
275(550) |
| GeForce 6200 |
4 |
3 |
64/128-bit |
GDDR/128MB/256MB |
300MHz |
275(550) |
** Not manufactured anymore - Spec are reference specification. Speeds can differ per model and manufacturer
In many ways the product is feature wise 100% similar to the entire 7800 series. This means you'll be able to select resolutions up-to a fantastic 2560x1600 (and actually play games at that resolution) thanks to the dual link DVI connectors.
| What is a shader ? |
| What do we need to render a three dimensional object; 2D on your monitor? We start off by building some sort of structure that has a surface, that surface is being built from triangles and why triangles? They are quick to calculate. How's each triangle being processed? Each triangle has to be transformed according to its relative position and orientation to the viewer. Each of the three vertices the triangle is made up of is transformed to its proper view space position. The next step is to light the triangle by taking the transformed vertices and applying a lighting calculation for every light defined in the scene. At last the triangle needs to be projected to the screen in order to rasterize it. During rasterization the triangle will be shaded and textured.
Graphic processors like the GeForce series are able to perform a certain amount of these tasks. The first generation was able to draw shaded and textured triangles in hardware. The CPU still had the burden to feed the graphics processor with transformed and lit vertices, triangle gradients for shading and texturing, etc. Integrating the triangle setup into the chip logic was the next step and finally even transformation and lighting (TnL) was possible in hardware, reducing the CPU load considerably (GeForce 256). The big disadvantage was that a game programmer had no direct (i.e. program driven) control over transformation, lighting and pixel rendering because all the calculation models were fixed on the chip. And now we finally get to the stage where we can explain Shaders. Vertex and Pixel shaders allow developers to code customized transformation and lighting calculations as well as pixel coloring functionality. Each shader is basically nothing more than a relatively small program executed on the graphics processor to control either vertex or pixel processing. |
Now then, our usual blurb: What are the major advantages of the Series 6 and 7 products? Well, feature wise we are looking pretty much at the same technology we have known for 14-15 months now. What you need to remember is that any Series 6 and 7 graphics card can achieve what a modern game expects from it. Obviously the keywords over the past couple of years has been "Shader technology." It really changed the way we look at games from a graphical "Point of View". It allows the game programmers to take games to a next level in both a visual and performance terms.
As always, that's the point where we land and quickly discuss on Shader Model 3.
Talking about Shader Model 3
If you program or play computer games or even recently attempted to purchase a video card, then you will have no doubt heard the terms "Vertex Shader" and "Pixel Shader". The step from 2.0 to 3.0 was a small one and most Shader Model 2.0 games can easily be upgraded to Model 3.0, which can bring more performance to that gaming experience. DirectX 9 was recently updated and we are going to see more and more support for 3.0 Shaders.
Is SM 3.0 technology a huge visual advantage over 2.0? Nope, not even the slightest bit. Yet any technological advantage is always welcome and preferred over a previous generation's development. What you need to remember about Shaders 3.0 is that it can and will be used only in several critical places where it can give a performance boost and graphics cards are all about performance my friends. Both ATI and NVIDIA now offer Shader Model 3 support in their new products. GeForce Series 6 and newer models and for ATI their X1000 series and newer models.
Talking about HDR
Another big trendy implementation that will bring games closer to a movie like quality experience is HDR.
Both ATI and NVIDIA
have been focusing extremely hard on HDR. They put a lot of money into their technology to support HDR in the best possible way and they should as it just is a fantastic effect that brings so much more to the your gameplay experience. HDR is something you all know from games like Far Cry. It's extremely bright lighting that brings a really cool cinematic effect to gaming. This effect is becoming extraordinarily popular.
Valve recently released a new HL2 level in the form of Half Life 2: Lost Coast. Go download it as it'll show and amaze you what HDR can do. The difference is obvious. HDR means High Dynamic Range. HDR facilitates the use of color values way beyond the normal range of the color palette in an effort to produce a more extreme form of lighting rendering. Typically this trick is used to contrast really dark scenery. Extreme sunlight, over-saturation or over exposure is a good example of what exactly is possible. The most simple way to describe it would be controlling the amount of light used present in a certain position in a 3D scene.



Half Life 2 - Lost Coast level. If you bought the game, available for free on Steam.
HDR is already present in Far Cry, 3DMark06, Splinter Cell: Chaos Theory and in Half Life 2: Lost Coast. It will be available in Unreal 3 and likely a large number of other games. Let the screenshots do the talking.