One of the items in a recent donation to the Computer History Museum was an IBM 650 computer. IBM announced this machine in 1953, and it used a magnetic drum for memory instead of core.
My first job when I graduated from UCLA in 1965 was at IBM Service Bureau Corporation. My mentor there was Dr. Chuck Fillerup. Chuck taught me a lot about programming while we worked together on several projects.
Chuck told me many stories about how challenging it had been for him a few years earlier to program the IBM 650, since memory was actually a rotating drum. The way a program transferred control from one piece of code to another could have a big impact on performance, especially if it caused the program to have to wait too much for drum rotations. I thought of Chuck when I set my eyes on the 650 sitting in the Computer History Museum warehouse.