In 1984, AT&T started to market their new digital (fully digital that is) PBX called the System 75. The System 75 was a fully new system that could handle infinite technologies such as ISDN, PRI, T-1, and later IP and packet switching. AT&T also marketed the System 85, which was a Band-Aid code version of the Dimension. The System 85 ran on whatever stored software that used for the Dimension, but it shared hardware compatibilities with the System 75. In fact the System 85 had some interesting features such as AUDIX “Unified Messaging”, ports could max out to over 30,000 extensions and support up to 40 attendant consoles. Well, not the 302 console I posted earlier, but a boxy one that was used for the Dimension.
Another system called the System 25 was based almost entirely on the Merlin system with the code, and features. The System 25 is much comparable to a Merlin Magix or Legend system of today, which eventually replaced this odd setup.
What was common with all the cards and the type of carriers is the boards were cross compatible and hardware for phone lines and trunks could be interchanged during a cutover to a larger system. There was a reason why there was color coded labels on the boards, back in those days System x5 systems required tone clocks, processors and auxiliary connections to be together, line cards and those alike could be free floating if the customer chose so. Later versions of the Definity system would not have color coded labels and the cards could go in whatever fashion.
This cabinet can weigh as much as a stainless steel refrigerator, about an 800 pound voice gorilla and can support up to 700 lines.
It’s kinda strange how the power unit is located right next to the processor and tape unit…wouldn’t that cause problems?
To the left and right of each shelf has a power supply, for each row, it uses two sources of power. What’s interesting in this first version they all have power on and off (or kill switches.) Newer versions had power in only.
The bottom area was changed to support battery backups, the power supply and it’s tone generator in later years of the Definity/MultiVantage/Communication Manager systems.
It’s safe to say the System 75 scaled horrifically in the beginning again with that 700 port limit. However with creative integrators, you could theoretically have thousands of extensions using multiple System 75 (or even 85) PBXes and link the systems with a Distributed Communications System which would allow feature transparency through multiple of mediums (microwave, fiber, copper, CO, etc.) The New York State Government was a classic example where their Albany network had about 80,000 or so ports/extensions/lines and this was their original setup when commissioning this type of systems in the late 80s, according to Network World. DCS gets lot of mentions in this tell all as this would be a selling point to sell this system to other customers.