The biggest single plated-media drum that I ever saw was a Univac FASTRAND II dual-drum unit (counter-rotating) that used movable heads in an interesting mechanical setup using levers, linkages and solenoids to decode an 8421-type binary position to a physical position of the heads. Said unit was hooked to a Univac 1108. Univac used drums well into the 1970s, IIRC. I think the FASTRAND II positioning mechanism was described in a 1960s FJCC report.
Said FASTRAND was equipped with microphones (known as a "ping" detector) to detect when heads hit the plated surface. I suspect that an oxide-coated drum would have turned the coating to brown dust in a short time.https://www.cs.auckland.ac.nz/historydisplays/FourthFloor/ReportsAndViewer/Reports/MagneticDrum.pdf The one I witnessed in operation was installed on the second floor of a rather elderly building bordered by a busy street. One of the problems dogging the installation is that the heads would "ping" every time a big truck passed by the building. ----------------------- Having bored everyone with an old story, I did a little patent prowling... http://www.google.com.gh/patents/US2820688 describes the manufacture of a drum unit. Iron oxide in a shellac carrier spread on a drum surface, then machined to the desired profile appears to be described. http://www.google.com.gh/patents/US2771595 describes the basic idea of using a magnetic drum to store digital information. https://www.cs.auckland.ac.nz/historydisplays/FourthFloor/ReportsAndViewer/Reports/MagneticDrum.pdf is an interesting document from ERA describing the magnetic drum One of the issues addressed by several patents is the stability of the bearings--apparently, slight irregularity in bearing construction (or wear) can result in disaster. Something to bear in mind. If one were re-working an old drum, the traditional way of getting a smooth even surface is to plate with electroless nickel, then machine and polish the surface to the desired finish. This works for any substrate, as electroless nickel is an auto-catalytic process not dependent on the electrical properties of the substrate. FWIW, Chuck
