How many pixel shaders does the GF4 have?

[McElvis]

Just a quick question -

How many pixel shaders does the GF4 have?
And what about the GF3, the Radeon and the Radeon 8500?


Thanks!

 

[Kristof]

There is no single definition of what a pixel shader is, so its hard to quantify into numbers - since a pixel shader from company x is not necessarily equivalent to a pixel shader from company y. Same holds true for the vertex shaders.

Probably better to talk about how many Arithmetic Units and how many Texture Sampling Units there are. And even then the question is how capable is the arithmetic unit and how many samples can the texture sampling units take.

I am affraid its no longer a simple thing to answer.

K-

 

[McElvis]

OK. Thanks for the clarification anyway Kristof.

 

[RoOoBo]

There is no single definition of what a pixel shader is, so its hard to quantify into numbers - since a pixel shader from company x is not necessarily equivalent to a pixel shader from company y. Same holds true for the vertex shaders.

Probably better to talk about how many Arithmetic Units and how many Texture Sampling Units there are. And even then the question is how capable is the arithmetic unit and how many samples can the texture sampling units take.

I am affraid its no longer a simple thing to answer.

K-

If vertex shader is the processing unit that handles vertex programs and pixel shader is the processing unit that handles pìxels programs then the GForce4 has 2 vertex shaders and 4 pixel shaders. I think Radeon 8500 has the same number too.

I don't see any problem with the definition of what is a vertex/pixel shader (a processing unit for somekind of program). The definition doesn't change with the implementation. Of course when comparing them you should know arithmetic units and other resources it has. The same goes when comparing two CPUs for example Athlon with P4, they have very different resources and arithmetic units but they are both CPUs.

 

[DemoCoder]

I believe the GF3/GF4 have two register combiner units configured with loopback so that an 8 instruction pixel shader takes 4 clock cycles. In any case, the throughput is 2 ops per cycle (vector ops, scalars can be done in parallel).

 

[RoOoBo]

I believe the GF3/GF4 have two register combiner units configured with loopback so that an 8 instruction pixel shader takes 4 clock cycles. In any case, the throughput is 2 ops per cycle (vector ops, scalars can be done in parallel).

Then what happens when you are using the pixel shaders? I think GForce3/4 have 4 pixel pipelines, two remain iddle while the other tow are using the register combiners?

 

[DemoCoder]

Pixel shaders ARE register combiners in the GF3/GF4 architecture. Pixel shaders, as you have been lead to believe, are not programs executed like assembly language. They are syntactic sugar used to setup multitexture blending stages and combiner units.

DX9 shaders are implemented completely differently.

Secondly, those are 2 combiners in loopback per pipeline. Each pipeline can do 2 ops per cycle.

 

[RoOoBo]

Pixel shaders ARE register combiners in the GF3/GF4 architecture. Pixel shaders, as you have been lead to believe, are not programs executed like assembly language. They are syntactic sugar used to setup multitexture blending stages and combiner units.

DX9 shaders are implemented completely differently.

Secondly, those are 2 combiners in loopback per pipeline. Each pipeline can do 2 ops per cycle.

Then it was I said, the 2 combiners are the hardware that executes the pixel shader 'programs' or configurations or whatever you want to call them. And there is a pixel shader per pixel pipe. Even if DX8.1 pixel shaders are based in register combiners that are configured using pseudoinstructions they still act as something that runs 'programs' because they can be 'programmed' that it is tell to do different tasks (or the same task in a different way). I don't see it has to be really CPU like code or hardware to be call them 'programs'.