The Bendix used a magnetic drum Each memory line had a read head and a write head. Normally whatever was read would be written immediately, and would then travel around with drum rotation until it got bach to the read head and repeat the cycle.
@freemo These were still the early days of computing. When did they first start using disks with addressable permanent random-access storage? I don't know, but the first I saw myself appeared on another computer years after this Bendix was made. The Bendix was donated to tge university in 1957 by Pioneer Electric on condition that ghey could continue to use it for transformer design calculations. I do not mnow how old it was when it was donated. I do know it had lots and lots of vacuum tubes.
I do know that this ever recirculating memory was basic to the machine's design.
There were a few short memory lines of only one or two or four wordsmlong. These were used the way we use registers now. And a few destinations were special circuitry instead of being regular memry lines. The one-word accumulator was two destinations -- one for the usual write process, where you could provide new data to replace what would otherwise be rewritten, and the other that you used to add to what otherwise would be rewritten. So by specifying that a data transfer was to happen for multiple word times, you would end up adding multiple words from the source memory line to the accumulator. One instruction, no loop, many numbers added.
The drum was treated as volatile memory.
@freemo
The wikipedia has a nice write-up:
@hendrikboom3 if its encoded magnetically though why would it have to read and re-write the byte. If the byte is unchanged cant it just stay on the drum head as-is? Again unless im missing something this just sounds like a hard-drive platter to me.