On Thursday, May 06, 1999 9:43 PM, allisonp(a)world.std.com [SMTP:allisonp@world.std.com] wrote: According to Pugh's "IBM's 360 and Early 370 Computers", in 1963 IBM was manufacturing both 30x50 mil and 19x32 mil cores (inside diameter x outside diameter). Allison's measurements match up with the larger size. According to the book, the IBM 7080 and 7094 used the smaller size. Thus, these cores were probably intended for either the 1401, or the 7090 if any of these were still in production in 1963. Does anyone out there have a 1401, or a 1401 core stack? Something I hadn't read of before: the 7090's core planes were immersed in oil to help with heat dissipation. I wonder whether there was a sticker on the machine (right underneath "Trained Service Personel Only"): "Change oil every six months or 100,000 punched cards". Another interesting point: The defect ratio of cores that reached the plane wiring stage was 1 out of 8,000. This sounds incredibly high, but IBM's core manufacturing facilities were state of the art. Imagine the difference between the process control used then, and current integrated circuit fabrication techniques! I'd very much like to see your schematics, once you're happy with them. Better late than never to learn about appropriate circuit designs. ---- John Dykstra jdykstra(a)nortelnetworks.com Principal Software Architect voice: ESN 454-1604 Enterprise Solutions fax: ESN 667-8549