[p3n1s]

> They always knew how to do it, for decades

Unless we're limiting to the purely theoretical this is quite the hyperbole and in that case applies equally well to the 56k modem.

Size and heat are also factors. The process nodes did not exist in the 70s and early 80s to produce the integrated circuits necessary. VLSI technically enabled DSL.

The idea that somehow the difference between 1960s integration and 1990s is "purely economic" is pretty silly. If only they threw trillions of dollars more into research in the 60s would we have had the Intel Pentium then rather than 30 years later, maybe, but that is a useless line of reasoning. Someone has to actually do the "science".

You need to actually design and produce a suitable line card equivalent for every subscriber that will support DSL speeds without taking up the space of an airport for it and the cooling. That didn't exist for decades before DSL was rolled out (which started barely a decade after it was patented).

> DSL technology was perfected before the 56K modem was even invented.

Considering that DSL standards continued to evolve after the 56K modem was obsolete this is also hyperbole.

The other thing not yet mentioned which is pretty fundamental is that DSL eschews the 3.3khz bandwidth of POTS.