A favorite recording artist shared this explanation he got from an astrophysicist friend: It might be an oversimplification, but it works for me. https://youtu.be/sNGUkdovn_8

Fortran and then APL on an IBM 360 targeted at modeling and numerical methods classes at university in the 70s. It's no wonder that I still can't code.

I believe the OP was referring to a tethered set up.