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I wanted to add to this topic since I'm old enough to remember the T-100. I worked as a GM Tech and at the GM Training Center and actually taught a class on the Techline Terminals. I found this thread because I was researching why certain IBM keyboards were selling for such wild prices.
Yes, the T-100 (and T-120 and many others) were IBM computers (referred by GM to as "Techline Terminals") that GM contracted to be built for the purpose of managing service information (service bulletins, updating the handheld scan tools, reflashing the eproms in the ECM's and so on). There was another machine that GM tried before the T-100, also built by IBM called CAMS (computer assisted maintenance system). It used a very early pre-pentium processor, a 5 3/4" floppy drive and had a touch-screen interface. It had dozens of cables specially made to connect to various parts of each car's wiring harness for computer-aided troubleshooting. The Model M keyboard (102 keys I think) was locked in the drawer and only the administrator and IBM had a key. I remember when our dealership got one of the first ones available and the dealer said it cost him $18,000. That would have been about 1989 or 1990. The CAMS system was short-lived and replaced by the T-1XX series machines. GM decided to abandon the idea of using the CAMS machine to troubleshoot the vehicle directly, instead the aim of the Techline Terminals was changed to support the tech by providing service information and as a link to update the Tech1 scanner. Oh, BTW, the T-100 had a 100Mhz processor and the T-120 was 120Mhz and so on. Some of these first terminals used Windows 3.1. Before these dealership terminals were available, it was impossible to re-flash a vehicle's software. A new prom had to be ordered through the parts department. As vehicles became re-programmable in the field, the Techline Terminals were the method of downloading the software into the Tech1 and then into the vehicle.
GM was very protective of their service software (Techline) and required dealers to buy their terminals directly from GM Tools, instead of a generic computer dealer (Gateway, Dell, or any others). GM claimed the specs were so critical to run their software that only computers bought from them would work properly; thus forcing dealers to pay exorbitant prices for really common hardware. There were hardware and software locks to prevent dealers and techs from using the software on other machines. Because of this, only IBM PC's were used in GM dealerships. Technology was advancing very rapidly at the time and the terminals had to be replaced every 2 or 3 years, so the old PC was usually discarded as they were usually pretty dirty from greasy fingerprints. That's why finding those keyboards today is so hard.
Hope that explains a little about the GM Techline terminals back in the pre-historic days. I wish I had kept all those old keyboards. Ha.
Thanks for sharing!! This is really interesting.