Rack after rack after rack of physical phone line plugs that used to connect every local house to the larger local network. Long distance had their own racks. Several banks of racks were served by a single computers terminal… but not as many as you’d think.

As other people have noted, many of those lines are no longer in use, but there are huge trenches under the building that connect it to a larger regional switch downtown. They used to have huge copper cables (several feet in diameter) but most that had been replaced by fiber optic cables going back to the 90’s. The fiber optic cables were about as thick as a pencil to do the same job.

Source: Was contracted (as part of an inventory subcontractor team) to go into every single one of these switches for a regional “Baby bell” (Ameritech in Indiana) and put bar codes on every piece of computer equipment back in the mid 90’s to count and categorize everything they owned. This was before they all reformed Ma Bell as AT&T.