It's the 1990s, and this extremely busy U.S. airport is adding a new concourse -- which means it's also time to upgrade the computers behind the trains that move passengers between terminals, says a pilot fish on the project.

"Each concourse has several door sets to match the number of doors on the train," fish says. "As the train pulls into the station, it must align itself with an antenna on the guideway so that the train's doors and the station doors line up perfectly. Then the station and vehicle doors can open together."

But it's definitely time for an upgrade. When the trains originally started operation in the 1980s, the door controllers were actually run by cheap home computers. A Commodore VIC-20, running a program written in Basic, opened and closed each door set.

And the fact that the two dozen VIC-20s are a decade old and no longer being made isn't the biggest issue with the setup. It seems the now-retired engineer who originally wrote the door-opening software for the VIC-20s is still collecting a fee to maintain it.

Twice a year he returns to fish's company, tweaks the software a little, loads the new software onto each of the VIC-20s, one at a time, and then sends the company his hefty bill.

The new concourse finally provides an excuse to improve that situation. It takes a single-board 486DX PC with a network connection, plus two weeks to write new controller software from scratch in C++ and test it against the company's simulation software, and the upgrade is ready to go.

"The field engineers removed all the 20-plus VIC-20s, installed the one 486 in a cradle and hooked it up to the network," says fish.

"And it worked flawlessly. That was more than two decades ago. As far as I know, it's still in place today."

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