Alex Hilleary from Cray Research talked about the STARTIO macro. He had to write his own IOS driver back at Cray when none of the IBM access methods would talk to his supercomputer (he is using an XA system as a fast I/O device).

Much of his lecture consisted of cautions; IOS does NO error checking when you use STARTIO, so you can make a mess of the operating system in a real hurry.

Since the access methods handle most of what we want to do, we don't have a real need for STARTIO. I've considered adding a command to the tape subsystem that would write tape marks to an offline device. This would require STARTIO since I can't do dynamic allocation in the subsystem address space. It's a research topic that I'll look into one of these days when I don't have anything else to do (HA!).