Is Gigatexel equal to a billion characters or a billion floats?
I am looking at an NVIDIA whitepaper on a GTX680 GPU . On page 6, the document mentions that the GTX680 has a fill rate of 128.8 gigatexels per second.
I have a few questions about this:
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Is one texel equal to one byte or four bytes? In other words, is it RGBA texel (or float) or just char?
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Is " 128.8 GB / s fill rate " the same as 128.8 GB / s bandwidth ?
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Gigatexels is a measure of the texture unit's throughput. Basically it is capable of 128.8 billion filtered texture samples per second.
1) Texel may vary in size as you say. The texture is often RGBA characters 4 (4 bytes), float (4 bytes), or 4 floats (16 bytes). There are other texture formats as well, and texel is data for a single texture point.
2) No. The amount of memory in GB / s determines how fast the GPU can "potentially" read from its main / global memory. If the texture samples are not coherent (i.e. don't use the same / adjacent texture section) then global sampling will be required and the main memory issue becomes a problem. This also applies to any data other than the Gigatexel figure and the fact that the vertex data is also read from memory. Having high throughput is critical, especially when there are many, if not thousands of cores requesting this data.
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