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The passage around this formula

With two verified anchor points — HBM3 in 2022 at roughly 0.82 terabytes per second per stack, HBM4 in 2025 at up to 2.0 terabytes per second per stack [ 1 , 2 ] — it is possible to build an explicit, falsifiable trajectory rather than a vague “bandwidth will keep rising.” Model the growth as a simple exponential in calendar time, $B(t) \approx B_0 \cdot 2^{(t - t_0)/\tau}$. where $B_0$ is the bandwidth at reference year $t_0$ and $\tau$ is the doubling time implied by the data. Solving for $\tau$ from the two JEDEC anchor points gives

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