The magnetic drum memory/storage is a fascinating precursor to RAM and hard drives, performing both functions simultaneously. The vacuum tubes only store the next set of processor instructions to be executed
Now think about doing that with bulky and hot vacuum tubes and you quickly realize that you can't have any reasonable quantity of RAM without making the computer the size of a room. The vacuum tubes are just your registers and you need to be clever with the memory and storage. This is also why we don't use SRAM very much even today.
Can you imagine what a leap forward Core Memory was at the time? Not having to wait on a spinning drum to get around to reading the memory line you needed is like going from hard drives to SSDs.
Also, if any old timers remember the Story of Mel this is the class of computer Mel was working on.