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IBM Token-Ring LAN connector

This is an original photograph by Andrew Alder, taken on 11 November 2003.

Permission is granted to copy, distribute and/or modify under the GFDL, version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts.

These 4-conductor hermaphodite connectors are now something of a curiosity!

They were never terribly successful. They contained a switching arrangement that was supposed to eliminate the need for a hub by shorting the connector when disengaged to maintain the integrity of the ring. This in theory enabled hot joining and leaving of the ring by physically connecting and disconnecting the machine. Not only did it fail to do this, but it also succeeded in crashing many hubs if they were installed. But provided the machine was powered up before connection, and down before disconnection, these same hubs would reliably manage hot joining and leaving. They even often survived hot-plugging and unplugging of running machines, provided a non-shorting connector was used instead of these. So the switching was a dead loss.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. Subject to disclaimers.