Until surprisingly late, each computer (and then computer system) was a custom-crafted device.

Even after somewhat "mass market" systems, the software was almost always entirely custom for the end-user.

The port in 1977 of Unix to an Interdata architecture was one of the singular accomplishments of the Unix operating system.

It was a very common thing until the world settled into PC vs Mac for the most purposes, until tablets and phones came to be.

For the last 20 years of his career, my dad worked on a program to attempt to migrate the IRS off their dependence on IBM 360 Assembly Language.

Apparently the current attempts to throw LLMs at the problem are running into the issue that there's very little open source IBM 360 code available to train on.