Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!ucsd!casbah.acns.nwu.edu!accuvax.nwu.edu!nucsrl!telecom-request From: kabra437@pallas.athenanet.com (Ken Abrams) Newsgroups: comp.dcom.telecom Subject: Re: Switching Office Open House Message-ID: <15304@accuvax.nwu.edu> Date: 8 Dec 90 23:55:35 GMT Sender: news@accuvax.nwu.edu Reply-To: Ken Abrams Organization: Athenanet, Inc., Springfield, Illinois Lines: 27 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 872, Message 2 of 13 In article <15250@accuvax.nwu.edu> rees@citi.umich.edu (Jim Rees) writes: >As a computer guy, one thing intrigued me. Can anyone tell me about >the "1ESS memory card" that is just a piece of aluminum the size of a >sheet of notebook paper? It doesn't seem to have any electrical >contacts, but you can see little squares on it that might be >individual bits of magnetic memory. Those are indeed very small magnets on the aluminum cards. This is something like EPROM on a huge scale. It is really quite a feat of precision mechanical engineering. To change the memory, the cards are put on a tray and "written" with a 44 head card writer mechanism. The whole process is a mechanical nightmare but it has proven to be very reliable over the years. The little magnets slide in against a mylar strip with very fine "read wires". On the other side of the mylar strip is a device that produces a weak magnetic pulse across a row of 44 bits. The ones where the adjacent magnet on the card is "off" will send the pluse through and produce a "1". If the little magnet is "on", then the pulse is blocked and a "0" is the result. The "words" come out 44 bits at a time. Ken Abrams uunet!pallas!kabra437 Illinois Bell kabra437@athenanet.com Springfield (voice) 217-753-7965