Right. It was really common for sites in the 1970s to compile their own OS so they could set the configuration. This was how you told it which devices where attached on which ports.
"compile their own OS"??? I thought SYSGEN is necessary. At least in 1990s when I supported these machines as OS (and later DB2) supports.
I suspect it is in general necessary even to these days, but whether they will start with MVS 3.8 and gradually build up to whatever machine we are onto, I am not sure.
