[silizium]

The speed of electrical waves in a chip is ~c/2.

The relative permittivity εr of SiO2 is ~4.

c = c0 / sqrt(εr)

c0 = 1 /sqrt(ε0εr × μ0μr) and in vacuum εr=μr=1.

But the frequency needs to be sufficiently high in order to observe wave propagation, let's say >10GHz.

For low frequencies the electric conductor behaves more like a RC chain.

[eqvinox]

Considering the PCIe context, I was assuming we were talking about off-chip connections, i.e. diff microstrips/striplines in FR4 and air. εr is 2.6-ish there.

But you're right, I might have accidentally mixed in some radio connection bits, with the HFT company anecdote.