Blackwell

Current obstacles

Physics limits

• Copper reaches only about a metre at top speedAt about 200 Gb/s per wire pair, electrical signals fade within roughly a metre of copper. That confines NVLink's all-to-all domain to one rack; going further needs optics, which cost power.
• Number formats can't shrink much furtherGoing from 16 to 8 to 4 bits roughly doubled throughput each step. Below about 4 bits, numbers can't represent weights and activations accurately enough, so this lever is nearly used up.
• Each die is already at the size limitEach Blackwell die is close to the 26 × 33 mm maximum a scanner can print. Growth now means joining dies, and the link between them costs chip area and energy for every bit that crosses it.