The Greenbook standard was written in 1991 with the collaboration of Advanced Micro Devices (AMD), Motorola, DEC and Synoptics. The Greenbook standard uses STP cables with 150 ohmimpedance, in particular the specified IBM Type 1 or Type 1A cables.
The coding used is a two-stage NRZ-I coding, Non Return to Zero Inverted (NRZ-I). As data connector the Sub-D connector is used in the standard, optionally also the RJ45 connector. The Greenbook version has restrictions regarding double ring applications.