data stored in moving rust, was Re: Remembering RAMAC

Rotating magnetic memory is one of the oldest data-storage technologies. Drums solve the flying-head problem; you can bolt the heads in place. Some are contact, but many have a fixed gap. Drums have lower latency, 1 revolution worst-case. Hence they were used as main memory for modest machines and "backing store" (2nd-level) for many 1st-gen machines. Didn't EDSAC have a drum backing store added? There was one in the ACE design. Late 1940's saw magnetic drums in use. I'm too lazy to go out to the lab to look [in books] but certainly, IBM did not invent the disk drive. They may have commercialized it first, but I doubt that even. Maybe they were the first "successful" but that's a stupid measure. BFD. Hand-wave -- it was obvious. Radial or axial -- sigh, this issue comes up all the time. Not axial or radial heads, but the myopia of 'today is the measure of yesterday'. There were plenty of fixed-head radial disks, like flat drums. Today, memory and disk "we all know" what they mean (memory=CPU local, disk=one-or-more-level-removed) , but that arrangement is not obvious and has only ruled for little more than half the time that computers have existed. 1963/earlier: "hundred million bit disk file... each housed in a 2-1/2 ton utility truck" http://wps.com/projects/ARTOC/index.html