This was many years ago - the firm wrote and sold accounting software for the AS/400, so while they were production machines, there wasn't really a 100% uptime

This was many years ago - the firm wrote and sold accounting software for the AS/400, so while they were production machines, there wasn't really a 100% uptime requirement since there weren't end-users involved. The UPS was there to tide us over short power outages, and ensure a clean shutdown (IPLs after a hard shutdown took a very long time, as the OS would have to verify the whole filesystem). Me and another guy were the only Windows programmers there. We put a friendly UI in front of the AS/400 via network calls (SNA APPC, later TCP/IP sockets) to an endpoint that the RPG guys wrote for us. Later, we wrote an Excel add-in to allow the users to access their financial data from the AS/400, and this became so successful that the entire company is now based around the same technology. Sadly, I don't get a percentage.