cctalk Digest, Vol 52, Issue 30

Date: Fri, 14 Dec 2007 14:52:29 -0800 From: "Rick Bensene" <rickb at bensene.com> I don't know--the drum on the IBM 650 spun at 12,500 RPM, was 4 inches in diameter and about a foot long. This is not a project I'd launch into lightly. In the 70's and 80's Meshna would occasionally offer a mil-surplus drum unit for sale usually from some some airborne installation (i.e. used in radar). Lots of heads and no guarantee. The precision necessary in the mechanicals is pretty daunting. The heads fly at a few micrometers above the surface of the drum, which pretty much mandates some sort of clean-room environment. The bearings would need close to zero runout and getting the surface of the drum coated smoothly enough, either by plating or with a magnetic emulsion would also be an obstacle. If you have a good precision machine shop and mechanical engineering skills at your disposal, you could try it. Personally, I'd rather work something up with a magnetostrictive delay line memory--easier to build and quite robust--and just as "vintage". I recall that even in the 70's, drums had their problems. On the CDC STAR, every so often, a station would go down because of a "drum error"--more frequently than the disk drives encountered errors. You could make the heads on a Univac Fastrand II drum "ping" just by jumping up and down on the floor near the monster. I also recall that the ADL folks at CDC were working on a "super drum"--a very high speed unit that spun in a vacuum(IIRC) to be used as a paging store for the STAR. I recall the Neil Lincoln mentioned that the time between the observation window being clear and coated with drum surface was typically a few minutes at best. There's a nice story about the Manchester Mark I drum here: http://www.computer50.org/mark1/gethomas/manchester_drums.html About the only item of the correct size and tolerances that's readily available today, it seems to me, would be the drum unit out of a laser printer or copier. I don't know if the OPC layer could be easily stripped off and replaced with oxide, but it might be worth a try. If you're really serious abou this, I'd be willing to donate a head Cheers, Chuck