My first job was as a COBOL programmer on an IBM mainframe (OS/370 I believe) for Xerox. The system was absolutely massive and incredibly difficult to navigate. There were thousands of files with names that only had 6 characters. So everything was a two-letter system code, followed by four digits. LP0456, OP0234, SB1245, etc.

Then, in each of those files the variables had similar names in order to cut down on unique identifiers. WP100, WP101, up to the max number you needed at any given time. It was a nightmare. There was as much external documentation to keep track of all of this stuff as there was code.

On top of that, you could only build programs overnight in a batch process with the rest of the system, which was run by a different team in a different country (Spain, I believe). So you would write your program in the day, phone up the guys in Spain and explain that there was a new program going in and you were responsible for it. Problem was, if your program failed to build it would hold up the whole system, which HAD to be up and running and live again by the morning. This meant that every time you made a change that went into the nightly build you also had to be on call.

I remember eagerly watching the build queue at 1AM, waiting for my file's turn. Then immediately shutting everything down and going to sleep the moment it was successful. If it wasn't successful, well, then you had to fix it on the spot and phone Spain again to tell them to give it another try. Unfortunately, you rarely knew why it was failing.