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The GPU has higher priority access to the 3.5GB section. To optimally manage memory traffic in this configuration, we segment graphics memory into a 3.5GB section and a 0.5GB section.
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However the 970 has a different configuration of SMs than the 980, and fewer crossbar resources to the memory system. “The GeForce GTX 970 is equipped with 4GB of dedicated graphics memory. Nvidia responded on Friday with this statement (and chart):
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