HiGame

On November 8, 2006, Nvidia officially launched its first unified shader architecture and first DirectX 10-compatible GPU, the G80. The new chip debuted in two new cards, the $599 GeForce 8800 GTX and the $449 GeForce 8800 GTS. Today, the 8800 GTX’s specs seem modest, even low-end, with 128 shader cores, 32 texture mapping units, and 24 Render Outputs (ROPs), backed by 768MB of RAM. But back in 2006, the G80 was a titan. It swept both Nvidia’s previous GTX 7xx generation and ATI’s Radeon X19xx series completely off the table, even in games where Team Red had previously enjoyed a significant performance advantage.

But the G80 didn’t just rewrite performance headlines — it redefined what GPUs were, and what they were capable of.
For this retrospective, we spoke with two Nvidia engineers who did a great deal of work on G80: Jonah Alben, Senior VP of GPU Engineering, and John Danskin, VP of GPU Architecture. Before we dive in, however, we want to give a bit of context on what made G80 so different from what came before. Beginning with the GeForce 3 and Radeon 8500 in 2001, both ATI and Nvidia cards could execute small programs via specialized, programmable vertex and pixel shaders. Nvidia’s last desktop architecture to use this approach was the G71, released on March 9, 2006. It looked like this:



G71 block diagram.

In this diagram, the vertex shaders are the eight dedicated blocks at the top, above the “Cull / Clip / Setup” section. The 24 pixel shaders are the large group of six blocks in the middle of the diagram, where each block corresponds to four pixel pipelines (24 pixel shaders, total). If you aren’t familiar with how pre-unified shader GPUs were built, this diagram probably looks a bit odd. G80, in contrast, is rather more familiar:



Nvidia’s GTX 8800 family were the first consumer graphics cards to swap dedicated pixel and vertex shaders for a wide array of simpler stream processors (SPs, later referred to as CUDA cores). While previous GPUs were vector processors that could operate concurrently on the red, green, blue, and alpha color components of a single pixel, Nvidia designed the G80 as a scalar processor, in which each streaming processor handled one color component. At a high level, Nvidia had switched from a GPU architecture with dedicated hardware for specific types of shader programs to an array of relatively simple cores that could be programmed to perform whatever types of shader calculations the application required at that particular moment.

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