GeForce 8 Series Architecture

Introduction

NVidia has just released their new GeForce 8 series, formerly known by its codename, G80. This new series uses a completely different architecture from all other graphic chips, using a unified shader engine. In this article we will explain in details all that is new on this new graphics chip series.

GeForce 8 is the first series to support the forthcoming DirectX 10 (Shader 4.0 model). So first let’s talk about what is new in DirectX 10.

One of the new things on DirectX 10 is geometry processing. Until now the system CPU was in charge of this task. On DirectX 10 geometry processing can now be done by the graphics chip. Geometry processing smoothes curved surfaces and you can see a better quality on character animation, facial expressions and hair.

DirectX 10 provides more resources to the GPU, improving 3D performance. The key differences in GPU resources between DirectX 9 and DirectX 10 you can see in the table below.

Resources	DirectX 9	DirectX 10
Temporary Registers	32	4,096
Constant Registers	256	16 x 4,096
Textures	16	128
Render Targets	4	8
Maximum Texture Size	4,048 x 4,048	8,096 x 8,096

In the table below you see a comparison between shader models 1.0 (DirectX 8.1), 2.0 (DirectX 9.0), 3.0 (DirectX 9.0c) and 4.0 (DirectX 10).

	Shader 1.x	Shader 2.0	Shader 3.0	Shader 4.0
Vertex Instructions	128	256	512	65,536 *
Pixel Instructions	4+8	32+64	512	65,536 *
Vertex Constants	96	256	256	16 x 4,096 *
Pixel Constants	8	32	224	16 x 4,096 *
Vertex Temps	16	16	16	4,096 *
Pixel Temps	2	12	32	4,096 *
Vertex Inputs	16	16	16	16
Pixel Inputs	4+2	8+2	10	32
Render Targets	1	4	4	8
Vertex Textures	–	–	4	128 *
Pixel Textures	8	16	16	128 *
2D Texture Size	–	–	2,048 x 2,048	8,192 x 8,192
Int Ops	–	–	–	Yes
Load Ops	–	–	–	Yes
Derivatives	–	–	Yes	Yes
Vertex Flow Control	–	Static	Static/Dynamic	Dynamic *
Pixel Flow Control	–	–	Static/Dynamic	Dynamic *

* As DirectX 10 implements unfied architecture as we will discuss in the next page, this number is the total for the whole unified architecture and not for this individual spec.

Besides the increase in resources capacity, there are several new features on DirectX 10, but in summary the goal of this new programming model is to reduce the system CPU role on 3D graphics performance – i.e., it tries to avoid the use of the system CPU as much as possible.

Of course we will have to wait until DirectX 10 games are released to see these new features in action. Some of the games that will be released based on DirectX 10 include Crysis and Hellgate London.

But the main difference between GeForce 8 series and all other graphic chips available today is its unified shader engine, another feature introduced by Shader 4.0 programming model. Let’s talk more about it.