DonsDaMan
Member
The following is entirely conjecture:
I think that back in the 1980's, when PLC's were still evolving, someone came up with a new style PLC. Instead of having a single box with X number of inputs of type M and Y number of outputs of Type N, some engineer came up with the concept of putting the data and address bus in a single rack, similar to the way many "rack mounted," systems were operating at the time.
Anyway, this engineer got the project to a point that the concept seemed to be an improvement on the existing I/O pre-defined PLC's that were the norm in industry. Marketing needed a way to show the world that this was the way to go.
Some bright marketing type said, "Let's call the old style the 'single unit' PLC, and our NEW one a 'modular' PLC." This got debated until "single unit" became the "Unitary" PLC.
Of course, at another company, they had a fixed number of slots pre-determined in their rack, and called it "rack mounted," again taking its cue from marketing.
Then, around that time, someone was making up the curriculum for some standardized testing. They said, "Hey, the people should know the difference between these systems, since the salesmen think it is so important..."
And the rest is history....
</conjecture>
I think that back in the 1980's, when PLC's were still evolving, someone came up with a new style PLC. Instead of having a single box with X number of inputs of type M and Y number of outputs of Type N, some engineer came up with the concept of putting the data and address bus in a single rack, similar to the way many "rack mounted," systems were operating at the time.
Anyway, this engineer got the project to a point that the concept seemed to be an improvement on the existing I/O pre-defined PLC's that were the norm in industry. Marketing needed a way to show the world that this was the way to go.
Some bright marketing type said, "Let's call the old style the 'single unit' PLC, and our NEW one a 'modular' PLC." This got debated until "single unit" became the "Unitary" PLC.
Of course, at another company, they had a fixed number of slots pre-determined in their rack, and called it "rack mounted," again taking its cue from marketing.
Then, around that time, someone was making up the curriculum for some standardized testing. They said, "Hey, the people should know the difference between these systems, since the salesmen think it is so important..."
And the rest is history....
</conjecture>
