Increasing the number of GPUs within a rack, such as from Hopper (8 GPUs) to Blackwell (72 GPUs) and Rubin (500+ GPUs), is constrained by physical factors like power delivery, cooling, and crucially, cable density. The physical space and bend radius of cables limit how many high-speed connections can be routed within a rack.

Impact: High. These physical limitations are a fundamental barrier to scaling compute density, forcing innovation in rack design and cabling to accommodate the ever-increasing demands of AI models.

In the source video, this keypoint occurs from 00:41:00 to 00:44:00.

Sources in support: Dwarkesh Patel (Host)