This programmer says that old PC's are more of a problem than embedded chips are. This was posted on Peter de Jager's forum.
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. . . I've done plant tours, although in my case it was food production plants. While the embedded chips (PLCs) themselves did not do much, if any, date processing, they were controlled by PCs running WonderWare process control sofware.
The typical response when I first came into the plants and met with the Plant Manager, the Chief Engineer, and the financial officer was "Gee, we appreciate your visiting us, but we don't have anything except the PCs and the midrange machine in the front offices. You're wasting your time." After the tour, the typical reaction was "Wow, we didn't know we had so much!"
The typical production line is controlled by PCs that were too old to be used in the front offices, so they got moved back to run the less complex software that controls the lines. I never once saw a Pentium-based machine, most of them were '386, '486, and even older clones. Once the line is running, you don't change anything, even the computer.