Just happened to be searching ebay...came across this, what is it? what was the Horizon system?
https://cgi.ebay.com/AT-T-HORIZON-1...%3A1|240%3A1318|301%3A0|293%3A1|294%3A50

That's for accessing programming in a Horizon PBX. The customer one was called a CSU the one pictured is for the techs it was a SAU. The 1A2 the seller has in the title is wrong, it had nothing to do with 1A2.

Jeff, don't buy it. I have several of them if you want to borrow one. It won't do anything but light up unless you have a Horizon switch to connect it to.

It is the technician's programming instrument for the AT&T/Western Electric Horizon PBX. It allows for not only programming, but for backup/restore via the tape drive. This was known as an SAU (Service Access Unit).

There was also a similar one that was more of a desktop console known as a CAU that allowed the system administrator to make programming changes. It was almost the same thing except that it didn't include the tape drive and looked more like a phone without the handset cradle.

The Horizon PBX was available in the 16A or 32A sizes, meaning one or two shelves. Capacities depended upon the installed station and trunk cards (circuit packs as they were called). Most card slots were fixed. There were a few universal slots that allowed trunk or station cards. This system was the baby cousin of the larger Dimension 400, 600, 1000 and 2000 systems. Horizon's architecture was loosely based upon the design of the 1AESS central office switch. It supported standard SLT devices or MET (modular electronic telephones) and was state of the art in the early 1980's. METs were supported by both Horizon and Dimension systems.

It was definitely one of the first hybrid systems, where is was a cross between a PBX and a key system. Of course today's definition of hybrid systems are a completely different can of worms.

Now that I've told you how to build the watch, would you like to know the time?

EDIT: As I was writing yet another novel, Bill answered Jeff's original question in two sentences. :rofl:

No...Ed, I just wanted to know what the heck it was

Ed I worked on a lot of Dimension Systems when I was in RMATS, don't remember the 600 or the 1000, what were they?

Jim, I believe that they were custom configurations for the government to use overseas at military installations. I think the 600 was exclusively for use on Navy ships. I had some docs for them, but they looked like the standard Dimension docs to me.

Jim...what is RMATS?

Remote Maintenance And Testing System

It was a group the remotely programmed and monitored the larger PBX's. They were put in place a year or two after the Dimension PBX came out.

EDIT: Now that I think about it, it may be Remote Maintenance Administration and Testing System. It's been awhile and all we ever called it was R Mats

Ther "offical title" was Remote Maintenance And Translation Service,Wow.
Ed You're probably correct because all I Remember was Dim 400 FP2,FP3,FP4,FP10,and then lasty was FP15 which covered all the features of the previous FP's. Then we had Dim 2000 FP7,2000 FP8, and then 2000 FP8 iss3, which again covered all previous dim 2000.
The Dim line was a good switch except you could not pass data Sta.-Sta. unless you called out and back in again.It was time domain pulse code modulated.Being senior Tech here in El Monte Ca. we did lots of software peeks and pokes it was a interesting and fun job.

Also which I forgot to mention was the Prelude which was basicly for the Motel sector. (different switch totaly)

I remember trying to do some trunk installtion programming with a CAU. That's when I found out about SAU's. In the early 90's they were selling for $300 and up! We farmed out the programming to a retired AT&T tech that just 'happened' to have one. Couldn't justify the purchase, when he did the job for $25 and we had no other Horizon work on the horizon . For a change, my decision was the right one! The only Horizon work we did after that was jacking them up and sliding a ZTD or ADIX in place of them. John C.