Why did the clock stop climbing?

A desktop chip in 2004 ran at 3.8 GHz (Intel's Pentium 4 570J). A laptop from this decade: about 3 GHz, measured on one core. From the Intel 4004 in 1971 (0.74 MHz) to 2004 the clock rose about 5,100 times; in the twenty years since, 1.6 times (6.2 GHz in 2024).

Every tick pushes charge through billions of switches, and that energy turns into heat. In 1974 Robert Dennard and his colleagues at IBM worked out the rule for shrinking a switch: make it smaller, lower its voltage with it, and it gets faster while "the power density remains constant". Chipmakers pushed the clock faster still, and by 2004 a chip gave off around 100 watts, about what a heatsink and a quiet fan can carry away. Then the voltage stopped falling: below a point the switches leak and never quite turn off.

Our arithmetic: keep the clock climbing anyway, with the voltage stuck, and every shrink doubles the heat in each square millimetre. From 2004's 1 W per mm², six shrinks reach 66 W per mm², more than the 63 W per mm² leaving the Sun's surface. In 2001 Intel's Pat Gelsinger warned of the same, as The Register reported it: chips "as hot as the surface of the sun by 2015" on the path they were on.

That's the power wall. The clock stopped, and the new switches became more cores: a laptop today has eight to sixteen (AMD's Ryzen AI 7 350 has 8, its Ryzen AI Max+ 395 has 16). Don't buy a computer by its gigahertz.

What did your first computer run at?

Sources: R. H. Dennard, F. H. Gaensslen, H.-N. Yu, V. L. Rideout, E. Bassous and A. R. LeBlanc, Design of Ion-Implanted MOSFET's with Very Small Physical Dimensions, IEEE Journal of Solid-State Circuits, October 1974; Mark Horowitz, Computing's Energy Problem (and what we can do about it), ISSCC 2014; Intel product specifications (Pentium 4 570J, 2004; Core i9-14900KS, 2024), the Intel 4004 datasheet and Intel's release of 8 March 2000; AMD product pages (Ryzen AI 7 350 and Ryzen AI Max+ 395, 2025), read October 2026; IAU 2015 Resolution B3; The Register, 6 February 2001; our own measurement and arithmetic.
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