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Inside a GPU Lab

AI Infrastructure series · part 3 · what an H100 does with one layer of an AI model

An AI model is mostly one operation repeated: multiply a big table of weights by the numbers coming in. Follow one such multiplication, for one layer of an 8B model, through an NVIDIA H100. Press Next to move a step, or Play to watch it run.

The chip: 132 streaming multiprocessors (SMs)

One warp: 32 threads doing the same instruction

Where the numbers are

H100 SXM figures from NVIDIA: 132 SMs, 128 CUDA cores and 4 Tensor Cores per SM, 256 KB of registers and up to 228 KB of shared memory per SM, 50 MB of L2 cache, 80 GB of HBM3 at 3.35 TB/s. The steps are simplified; real software fuses several of them.

The same job on four kinds of processor: multiply two 8,192 × 8,192 tables of numbers, about 1.1 trillion multiply-and-add steps. This is the kind of work every layer of an AI model does, over and over. Times are at each processor's published peak speed.

Slowed down so the fast lanes are visible.

Peaks: 64-core server CPU about 5 TFLOPS in FP32 (illustrative, varies by model); H100 SXM CUDA cores 67 TFLOPS FP32; H100 Tensor Cores 989 TFLOPS in BF16 and 1,979 TFLOPS in FP8 (dense, NVIDIA). Real code reaches a share of peak; the order does not change.