Death Match

The others began to return. First, Sheldrake, shaking his head to indicate he’d found no alternate escape route. Then Dorfman and Lawson, who reported that, as expected, the backup generator and its power conduits were impervious to any attack they could mount. Last came Gilmore, soot-blackened and wheezing, to say that — while the sprinklers in the upper floors of the penthouse could be jury-rigged — the task would take an hour, maybe more, and would probably be insufficient to quell the dozens of fires that were now sprouting up all around them.

“An hour,” Sheldrake said through gritted teeth. “We’re lucky if we have ten more minutes. It’s got to be a hundred and twenty in here, at least. Those battery cells could go at any time.”

Nobody had a response to this. The air was growing so hot, the smoke so thick, Lash found it nearly impossible to breathe. Each time he drew in air, sharp needles filled his lungs. He felt his head grow light, his concentration slip.

“Just a minute,” Tara said. She had stepped forward and was standing directly before the control surface of the IBM 2420. “These buttons. Each one is labeled with an assembly language mnemonic.”

When there was no response, she looked over her shoulder at Silver. “Isn’t that right?”

Silver coughed, nodded.

“What are they used for?”

“Diagnostics, mostly. If a program didn’t work, you could step through the opcodes, sequentially.”

“Or enter new instructions by hand.”

“Yes. They’re an anachronism, a holdover from an earlier design.”

“But they do allow access to the accumulator? The registers?”

“Yes.”

“So we could run a short instruction set.”

Silver shook his head. “I’ve already told you. Liza’s defenses won’t accept any new programming. Any input from the card reader or keypunch would activate a security alert.”

“But I’m not talking about entering a program.”

Now Mauchly turned to look at Tara.

“We wouldn’t input anything from a peripheral. We’d punch in a few opcodes, right here. Five — no, four — should be enough. We’d just run those four opcodes, over and over.”

“What four opcodes are those?” Silver asked.

“Fetch the contents of a memory address. Run a logical AND against those contents. Update the memory address with the new value. Then increment the counter.”

There was a silence.

“What’s she talking about?” Sheldrake asked.

“I’m talking about accessing the computer’s memory in the most primitive way. Byte by byte. Doing it manually, from the computer’s own front panel.” Tara glanced back at Silver. “The 2420’s an eight-bit machine, right?”

Silver nodded.

“Every location, byte, in the computer’s memory has eight bits. Okay? Each of those bits can have one of only two values: zero or one. Together, those eight binary numbers make up a single instruction, a word in the computer’s language. I’m talking about zeroing out all those instructions. Leaving the computer blank. Instructionless.”

Sheldrake frowned. “How the hell could you do that?”

“No, she’s right,” said Dorfman, the security tech. “You could ‘AND’ a zero byte against each memory location, in turn. It’s almost elegant.”

Sheldrake turned to Mauchly. “You know what they’re talking about?”

“AND is a logical instruction,” Dorfman went on. “It compares each bit to a value you furnish, and either leaves that bit alone or swaps its value, depending.”

“It’s simple,” Tara added. “If you AND a zero to an existing zero in memory, it leaves it alone. But if you AND a zero to an existing one in memory, it changes it to a zero. So with the simple instruction—‘AND 0’—I can change any memory location to zero.”

“And that would leave you with NOPs,” Mauchly said, nodding.

“No Operation.” Dorfman’s voice rose with excitement. “Precisely. Leaving the computer’s memory full of empty instructions.”

“It wouldn’t work,” Silver said.

“Why not?” Tara asked.

“I’ve already explained. There are a dozen virtual simulacra of this machine, ru

“That’s just the point,” Tara said with a cough. “We’re not introducing any new programming. We’re just resetting the computer’s memory. Manually.”

“Out of the question,” said Silver.

Lash was surprised by the sharpness of Silver’s answer. For what seemed a long time — since Liza had gone silent, perhaps even before — Silver had acted defeated. Resigned. But now, there was a fierceness in his voice Lash hadn’t heard since their first confrontation.

“Why?” Tara asked.

Silver turned away.

“Can you tell me for sure—for sure—that you took that specific possibility into account when you coded the security protocols?”

Silver folded his arms, refusing to answer.

“Isn’t there a chance that zeroing Liza’s original memory will abort this self-destructive behavior? Or, at the very least, cause a system crash?”

Again, the question hung in the air. And now, for the first time, Lash made out a large gout of open flame — ugly orange against the black smoke — flaring up from a rack of equipment near the far wall.

“Dr. Silver,” Mauchly said. “Isn’t it worth a try?”

Silver turned slowly. He looked surprised to hear Mauchly voice such a question.

“Hell with it,” Tara said. “If you won’t help me, I’ll do it myself.”

“Can you program this thing?” Lash asked.

“I don’t know. Legacy IBM assembler didn’t change that much from machine to machine. All I can tell you is I’m not going to stand around, waiting to die.” And she stepped up to the archaic control surface.

“No,” said Silver.

All eyes turned toward him.

He’s not going to let her do it, Lash thought. He’s not going to let her stop Liza. He watched, transfixed, as the man seemed to wage some desperate i

Ignoring him, Tara raised her hands toward the row of buttons.

“No!” Silver cried.

Lash took an instinctive step forward.

“You need to deal with the parity bit first,” Silver said.

“Sorry?” Tara asked.

Silver fetched a deep breath, coughed violently. “The 2420 has a unique addressing scheme. The instructions have nine bits instead of the usual eight. If you don’t mask out the parity bit as well, you won’t get the empty instruction you want.”

Lash’s heart leapt. Silver’s getting on board, after all. He’s going to help.

Silver walked to a nearby teletype, snapped it on, threaded the attached spool of paper tape into the plastic guide of the reader. Then he moved behind the main housing of the 2420, his step increasingly decisive.

“What are you doing?” Tara asked.

Silver knelt behind the housing. “Making sure this computer will still respond to manual input.”

“Why?”

Silver’s head reemerged above the housing. “We’re only going to get one chance at this. If we fail, she’ll adapt. So I’m going to dump the current contents of her memory to paper tape.”

Tara frowned. “I thought you said you didn’t have any back doors.”

“I don’t. But there are a few early diagnostic tools, hard-wired, no hacker could ever have any use for.” Silver ducked back behind the housing. A moment later, the teletype came to life. The faded spool of tape began moving through the machine punch. A shower of thin yellow chads rained down onto the floor beneath.

Within a minute, the process was complete. Silver pulled an extra length of bare tape through the punch, ripped it away. He ran the tape through his fingers, sca

“Then let’s get on with it.” Behind Tara, more gouts of flame were rising, and her dark hair was backlit with angry flames.