Bey Wolf had inherited a good stubborn streak from his German father and a subtle and suspicious mind from his Persian mother. Both parts of the combination were needed now. He was stuck in the middle of a rank impossibility.
He had analyzed defective form-change runs. They ranged from minor flaws too subtle to be detected in outward appearance to grotesque end forms that could never have survived in any environment known to Bey. Every one was different, but in one way all were alike. The ferret routines he had introduced into the purposive form-change programs confirmed that there had been systematic modifications to whole sections of code; they pointed always to the same impossible blind alley. The changes were no accident. They were so complicated that they had to have been generated by a computer—but in a place where no computer capability existed on the harvester.
He swore and grumbled and grunted to himself. His work had gone on obsessively for several days, broken only by hurried meals and occasional naps. He had not washed or changed his clothes. He was surrounded by empty disposable plates and cups, listings, diagnostic trace routines, system flow diagrams, and his own scribbled notes and questions. Paper was everywhere, sprawling across the floor and over every available surface.
Bey was totally frustrated and oddly content. No one on the harvester could help him, and he did not want help. He wanted to solve it himself. He did not admit it, but intense concentration was also a form of therapy. He wanted to keep the disturbing thought of Mary Walton’s visitation out of his head.
Sylvia Fernald had stopped by a couple of times in the first day of work. She had watched his efforts sympathetically, spoken to him, and left when it was clear that his mind was elsewhere. On the third day Leo Manx had also appeared. He came to the door of the room several times, stared in disgust at the mess, and hobbled away. The wounds he had received on the space farm were not yet fully healed, but he was in no apparent discomfort.
When Leo came by for the fourth time, he stayed, standing silent in the doorway and puzzling over a blue folder he had brought with him. Bey Wolf ignored him until a final and irrefutable statistical analysis came back on the display screen. At that point he swore at length, switched off the unit, and turned to the other man.
“That does it. I know exactly what happened—and I’ve no idea how.”
Manx looked up from his own musings. “If you’ve discovered anything useful, you’re making more progress than I am. What have you found? Cinnabar Baker will want to know.”
Wolf waved his arm at the sea of listings covering the floor around them. “I have output trace listings of everything. Do you know how the harvester computer system works?”
Manx frowned at the question. “Well, I feel sure it’s a straightforward distributed system. There’s computing capacity and major storage in a couple of hundred nodes located at different points in the harvester, and local storage with limited compute power at a few hundred more. Everything is tied together through a fiber communications system. It’s exactly like the integrated computer system on the other harvesters—or in your own Office of Form Control, back on Earth.”
“My ex-office. So there’s nothing unusual about the arrangement?”
“Of course not.” Manx had stepped gingerly into the middle of the paper jungle and was carefully collecting the listings into neat piles. “Bey, you must have known all this days ago—you couldn’t generate these message traces without knowing.”
“I thought I did.” Wolf grabbed an elaborate schematic. “The general structure is shown here. I took this, and I began to search for places in the system where spurious coding sequences could be introduced to modify the form-change programs. Watch now.”
He switched on the wall-size display screen. “I’ve color-coded this. You need to know what they mean. The blue network is the overall connection plan for the distributed computer system. The red nodes show where we have data storage; green ones show computer elements. Purple dots are sensors—data collection points for the computer system. Orange dots are form-change tanks. They have some of their own storage and computer power, but they rely on the master system for some data and computation. Understood?”
“Perfectly. I hope there’s a point to all this.”
“There is. Just watch. I spent days working it out. You’re going to see my ferret routines, chasing down all the places where false code might have come into the system. We’ll do just one case now, for a form-change anomaly they had in the resource control office of this harvester. Watch the moving yellow tracer.” Bey entered the command and leaned back in his chair.
For a moment or two the display was static. Then a fine yellow line appeared at one of the orange dots and crawled across the screen. It reached a green node and divided there, then two yellow daughter traces continued on their way to a red element of the schematic.
“Picking up data from two different banks,” Bey said. “That happens a lot.”
The yellow lines crept onward, reaching new computer nodes, sometimes branching, sometimes terminating there. After thirty seconds a complete tree structure had been established, starting at a single form-change tank and spreading across half the screen.
“That’s one complete form-change operation,” Bey said.
“It’s too complicated. I can’t follow all that structure.”
“Nor could I, without help. The central controller used whatever computer power happened to be available—that’s why you see so many green nodes in use. It’s a horrible mess. Now, I’m going to add the other hundred and fifty-six cases, all at once. You’d expect the picture to become even worse, impossibly complicated.”
“It’s impossibly complicated already.”
“I agree. But it simplifies. Watch.” Bey entered a new command. The whole screen lit up with a tracery of moving yellow lines. They each began at a form-change tank and branched and zigzagged across the display. Thirty seconds later the screen steadied. Leo Manx shook his head. Lines were everywhere, a tangled mass of knotted interconnections, convoluted and horribly interwoven.
“I hope you don’t expect me to read anything useful out of that.”
“With a little help you will.” Bey was busy again at the terminal. “I agree it still looks like a gigantic mess. So I wrote another program to help sort it out. I asked for a statistical analysis of the places where each branching set ended. That would tell me how often the form changes were using a particular data storage bank, or a particular computer. If one storage area or computer was receiving unusually heavy use, that would be a good place to do some troubleshooting. Take a look at what I found. The program flags every terminating node that occurs more than two sigma away from the mean for all nodes.”
A couple of dozen points on the screen began to blink. Leo Manx stared at them blankly. “Very interesting,” he said after a few seconds.
“You’re wrong. It is interesting—once you look at those nodes more closely.” Bey stood up and went to the wall display. “Some end at computer elements; some end at data banks. Very reasonable. But what about this one?” He was pointing at a flashing purple point on the screen.
“What about it?”
“Leo, remember the color code. Purple. That means it’s a sensor—a place that collects data for the computer system.”
“That’s not surprising. There are sensors on each form-change tank.”
“True. Not surprising—if this were a sensor associated with a form-change tank. It would be collecting physical readings from the tank and using them in the programs. But this sensor should have nothing to do with a form-change process. And every form-change anomaly has a branch that ends there. That sensor was involved every single time we had a form-change problem.”