> The thing is that there was a lot about those old systems that was slow, so you were very, very careful how you programmed.

That's a common sentiment. I wish I could find the quote by someone who made the transition; it was about how happy they were to be able to compile so much quicker, and how getting immediate feedback made them so much more productive.

I recently had to put together a small program with JCL for work, and had real difficulty in finding documentation. Can you recommend anything?