But this would not give you a supercomputer, because most big problems aren’t embarrassingly parallel. Instead, the processors need to send intermediate results to each other, and a supercomputer must be able to parallel-process general problems and solve them faster, as well as being able to process many independent, little problems at once. This is what makes it different from a loose network of computers, and from a mainframe computer.
How good is the network?
The parallel performance is limited by the quality of the network, in particular two features:
• bandwidth—the amount of data it can carry per second, which we would like to be big
• latency —the delay between sending and receiving, which we would like to be small.
“So one is alive and one isn’t,” said George, catching on quickly.
“That’s right,” confirmed Annie. “But what’s the difference?”
“Erm … ,” said George, baffled. “One of them can choose his own actions and the other can’t?”
“Nope,” said Annie. “Ebot’s got a control panel, but he can also learn from previous commands in order to determine his own movements.”
“One needs food, sleep, and water; the other doesn’t?”
“Ebot needs energy too,” said Annie. “And you can’t say that my dad really sleeps.”
“True … ,” mused George. Eric was famous for only needing about three hours’ sleep a night—a fact that all his neighbors were only too well aware of: he played loud opera music in the small hours while he was working. “Where’s Ebot now?”
“Recharging,” said Annie.
“One of them breathes,” George suggested, “and the other doesn’t? One has things like a stomach and a heart, and the other has wires and stuff inside?”
“Yeah, that’s what I thought!” said Annie. “I’m taking a look at what each one is made of. I’m making a list of the elements of life.”
“What’s number one?”
She scrolled down past the pictures of the two Erics to a banner headline that read CARBON.
“Everyone knows,” George read out loud, “that carbon comes from stars. Hmmm …” He paused.
“What?” said Annie, self-conscious now that George was reading her work out loud. “Have I made a mistake? I spell-checked it.”
“No, the spelling is fine,” he told her. “But I just don’t think everyone does know that about carbon.”
“Oh, Okay …” She erased the line on Cosmos’s screen and started typing: Az most peoble no—
“You’ve put a b,” said George. “It should be a p.”
“I thought it was on autocorrect!” exclaimed Annie. She pressed a few keys to switch the function on.
“But the point is,” continued George, “I don’t think people know much about carbon at all. I mean, you and I know that carbon comes from stars, because your dad got Cosmos to show us what happens when a star reaches the end of its life: there’s a great big supernova explosion. But I don’t think most people know that the elements are made in stars.”
You might not know, Annie wrote, the computer now correcting her spelling as she went along, that carbon comes from stars. One of the important elements made in a star while it is burning is carbon, and when the star dies, the carbon gets sent out across the universe and can become other things, like you and me. We are “carbon-based” life forms. Carbon—
“Are you going to say what carbon actually is?” interrupted George. “Otherwise people are going to read this and think they’re made of lumps of coal.”
WHAT IS A SUPERCOMPUTER?
Using computer memories
There are several different ways today of connecting processors together to create supercomputers.
Symmetric Multiprocessor (SMP) systems
This system connects all processors equally to all the memory inside the supercomputer. They are also shared memory systems because the memory is shared between all the processors. It is difficult to do, and very expensive for large systems.
Nonuniform Memory Access (NUMA) systems
These networks become slower when the processor and the memory it wants to read or write to are farther apart. As they also have shared memory, the programmer has to be careful to keep data as close as possible to the processor that needs it. They are cheaper to run than SMPs.
An interconnect
This is a special, high-quality network that can connect a group of separate computers (referred to as nodes). The processors in one node cannot see the memory in other nodes at all, as the memories aren’t shared; these are distributed memory supercomputers. The programmer has to program the transfer of data as messages between the nodes. When the nodes are just ordinary computers rather than special modules, such supercomputers are often referred to as clusters.
Modern computer systems
It is common for modern computers to contain some of the parallel features once found only in supercomputers. For example, a single processor may now contain several cores, each of which functions as a processor in its own right—the processor becomes a SMP system, with multiple cores connected to a block of nearby memory. More expensive computers have more than one processor socket, so that each becomes a NUMA system, with a set of cores and a block of memory associated with each socket.
Graphics Processing Units (GPUs) for supercomputing
This is a recent development—perfect for anyone who likes gaming on their computer. They are very fast at creating pixels to send to your screen during a PC game. And the same design makes them very fast also at certain types of computation.
From flops to exaflops!
• 1 megaflop = 1 million flops
• 1 gigaflop = 1 billion flops (1,000 megaflops)
• 1 teraflop = 1,000 gigaflops
• 1 petaflop = 1,000 teraflops
• 1 exaflop = 1,000 petaflops
Using this measurement and looking over just the past few decades, it is easy to see how computer performance has improved:
• 1998: a computer with one processor might have a peak performance of 500 megaflops
• 2007: lots of single processors were rated at around 10 gigaflops
• 2013: single computers with two processors are available, each with eight cores, with a theoretical peak performance of 20 gigaflops per core, giving a total peak performance per machine of 320 gigaflops. This is actually a NUMA, shared memory, sixteen-core parallel machine in its own right—but today we wouldn’t call it a supercomputer unless we connected several hundred similar units together.
• The Top500 (www.top500.org) is a list of the world’s five hundred most powerful supercomputers, updated twice every year. At the time of writing, most machines on the list give a measured performance of a few hundred teraflops—but the top machine achieves a massive 33,862.7 teraflops (33.8627 petaflops). This is massively more powerful than the computers available at the end of the twentieth century!
In a few more years, it is probable that the first exaflop supercomputer may appear. How powerful is that!
“Yeah, yeah, I’m getting to that part,” protested Annie. “I do know what carbon is, by the way!”
“Then what is it?” asked George, who genuinely wanted to know.
“Well,” she said. “It’s like this …” She stopped typing and just talked. “Carbon,” she said, “has the atomic number six, which means that it has six protons and six electrons. The bond that carbon forms with itself is very strong: compounds containing bonds like this are very stable. The bond also allows carbon to form long chains and rings, better than any other element. This means that there are more known molecules containing carbon than all the other elements put together—apart from hydrogen. And it’s the fourth most common element in the universe,” she added.
“Wow!” said George. “You weren’t kidding.”
“I can’t be a chemist and not know about carbon,” replied Annie. “That would be like Mom trying to play the violin without doing
her scales. Or baking a cake without eggs. It just wouldn’t work.”
Up until that moment, the music from upstairs had been melodic and beautiful. It stopped for a second when a distant phone beeped with a message. Then the kids heard a great squawk as Annie’s mom played a horribly tuneless chord.
“Annie!” A few moments later Susan appeared at the study door, a look of shock on her face. “What do you know about the free airplane flights?”
“What free flights?” exclaimed Annie.
“All flights are free!” Susan held out her phone so the kids could read the message.
G’day, rellies! Whole gang on way. Got free flights. Cya soon, my darlings. Harroo!
“But what does it mean?” said Annie, checking her own phone. “I don’t believe it but it’s true! All flights are free! Can we get one? Can we go to Disneyland?”
“No, we can’t! Because my whole family”—Susan looked rather green—“are now coming over from Australia.”
“When are they arriving?” asked George.
“I don’t know!” she said in a panic. “My sister only said ‘soon’! It could be any time. All of them! Oh my goodness! In the next message they say they’ve decided to come as quickly as possible in case the free flights were a mistake and get cancelled.” She flicked on the small TV in the corner of Eric’s study. It was tuned to the news channel.
“International chaos at airports around the world,” said the announcer, looking worried as, behind her, footage showed airports deluged by people trying to push their way into the terminals with their baggage, “as airlines sell tickets for nothing. Major world airlines were surprised to find that their websites had taken overnight bookings for all international flights, all charged at the same price: zero. Passengers have raced to snap up the free tickets and are now attempting to travel on the cheapest flights the world has ever seen… .”
“How many of them are coming?” asked George. He’d only ever associated Annie’s family with peace and quiet; with learning, music, and technology. It was a surprise to find that a whole new branch of them was arriving from the other side of the world.
“Mom’s sister has seven kids,” explained Annie. “I’ve never met them, but they sound really fun,” she added longingly.
“Oh dear, oh dear!” fretted Susan. “This is going to be very difficult. And your father’s not here. I suppose it will take them at least a day to arrive, so perhaps he’ll be back by then… .”
“Perhaps they won’t notice that Ebot isn’t him?” said Annie.
“Don’t be silly, Annie,” her mother snapped. “Of course they’ll notice. They’re hardly going to mistake a robot for the real thing!”
“But Eric said that Ebot is very nearly the same as him, except for not being actually alive: lots of types of technology wouldn’t be able to tell the difference between them,” George supplied helpfully.
But to judge by Susan’s expression, he hadn’t said the right thing. “I think they’ll notice,” she said firmly.
At that moment Cosmos sneezed again.
“And what is wrong with that computer?” demanded Susan.
“He’s been a bit slow this morning,” complained Annie.
“I don’t feel well,” said Cosmos miserably. “I think I’ve caught something.” He sneezed three more times and then gave a feeble cough.
“I hope he hasn’t picked up a virus on the Internet,” said George, worried. It wasn’t like Cosmos to be this listless.
“Should you be using it when your father isn’t here?” Susan fretted.
“Oh please, Mom!” begged Annie. “I need Cosmos to do my chemistry project. I really, really, really have to get it done this vacation, and it has to be amazing! It’s super-important to me—I can’t fail!” She was pleading now.
George was taken aback to see that she had real tears in her eyes. He wondered why school was suddenly so important to her. With all these exciting relatives arriving from the other side of the world, he thought she’d forget about her project and get swept up with making plans for her family.
“Oh, all right… .” Annie’s mom wouldn’t usually have agreed to let George and Annie have free rein with Cosmos, a computer she considered dangerous and subversive. But the prospect of so many of her relatives showing up in the near future meant she wasn’t thinking straight.
“Where am I going to get enough sleeping bags?” she worried as she headed back into the hall. “And I’ve got a whole new symphony to learn… . These airlines have really messed up everyone’s lives. How are we going to fit another nine people into this house?”
“At least you won’t be lonely anymore,” George pointed out. “That’s good, right?”
“No—and hurray!” said Annie cheerfully. “Not lonely, for sure. Lots and lots of friends to play with! You can hang out with us, George.”
“No thanks,” he said. “Sometimes I’m not sure I like people that much. I think I prefer machines.”
Cosmos sneezed again.
Annie’s mom put her head back round the study door, looking flustered. “Now, Annie and George … I know this isn’t how we usually do things, but this is a sort of emergency. I’m trusting you to be very grown up. I’m going out, and I want you to promise me that you will be responsible and good while I am gone—especially with everything that’s happening. I want you to stay in the house. You can get on with your chemistry project, Annie. I’ll be back as soon as I’ve bought bedding and supplies. Do you promise?”
“We promise,” chorused George and Annie.
“I don’t think they can possibly turn up while I’m out, but if they do … ,” Susan shouted back over her shoulder as she ran toward the front door. They heard it slam behind her.
“If they do … what?” said Annie, looking at George.
“Feed them dinosaur toenails and take them for a nice spacewalk,” he suggested with a wicked grin.
“A spacewalk!” cried Annie. “That’s what we should do!”
“Oh no—hang on a minute,” said George. “I didn’t mean …”
They both looked at Cosmos, sniveling on the desk.
“I’m sure it would make Cosmos feel better,” wheedled Annie. “I expect he’s feeling bad because we haven’t used him lately. After all, he is a supercomputer, not just any old ordinary computer.”
George reflected that this was one of Annie’s more unlikely explanations. They hadn’t been allowed to go on any space expeditions for quite some time now: Eric had introduced some new super-rules over the use of Cosmos after Susan had been very clear that she would not tolerate any more perilous adventures.
“And we would be working on my chemistry project, after all,” said Annie. “My super-important chemistry project, which has to blind everyone with its brilliance when I go back to school next week. It’s got to be the most incredible piece of work I’ve ever done—we have to make it truly fabulous!”
“Do we?” asked George. “Why?”
“Well, I know I’m very clever and everything, but even so, it’s time for me to prove it. Now that I’ve done carbon, I’ve got to do my next entry, and I want to write about water in space. So we have to go and investigate, or I won’t have anything to say! And we wouldn’t actually be leaving the house… .”
“Well, we would really,” said George, “if we went into space… .” He was longing to go, but he still needed convincing. He was naturally more cautious than Annie, and he didn’t want to be banished from her house for misusing the space portal, either. It was all very well for Annie … she lived in the same house as Cosmos and would always, one way or another, have access to him. The same could not be said for George himself.
“No we wouldn’t!” said Annie. “Mum meant don’t go out into the street. She didn’t say don’t go out into space!”
Before George could object any further, she started typing rapidly on Cosmos’s keyboard.
“What if your mom comes back and we’re in space?” he asked. “How woul
d we know?”
“Good point!” Annie jumped up and ran out of the room, returning quickly with the haptic gloves, and Ebot following behind.
“He’s working now,” she said. “Say hello to George.”
Ebot raised a hand in greeting. “Hello, George,” he intoned.
Annie took off the gloves and handed them to George. He was quickly coming round to her idea. “Shall I put these on under my space gloves?” he asked her.
She grinned. “Good idea! You never know when we might need to operate Ebot remotely. Ebot, sit there… .” Annie pointed to a spare chair from where he would be able to see both Cosmos and the door. Then she grabbed the remote-access glasses from the table by Cosmos.
“While we’re in space,” she explained to George, “I’ll be able to see through Ebot’s eyes. So if Mom comes home, we’ll get an early warning and come back to Earth tout de suite!”
As she talked, Cosmos was already creating the space portal. Two narrow beams of brilliant light shot out of his screen, picking a point in the room from which they moved in opposite directions to outline the shape of a doorway.
Meanwhile Annie rifled around in the large cupboard where her dad kept the space suits.
“Here’s mine!” She came across a suit that she had customized with ribbons, glitter, and badges. “But where’s yours?” She threw a few others out of the cupboard. “I can’t find it! Here—take this one.” She chucked him one of the random suits.
“That’s your dad’s!” said George. “I can’t wear that! It’s got his insignia and call sign! If I use the voice transmitter, it will look like Eric is in space!”
“Stop wasting time!” Annie was impatient to get going. “We’re only going to nip out to space for a few minutes. It’s not like NASA will notice.”
The space door Cosmos had created was now swinging open very slowly. Annie and George could just see a faint glimmer of the world that lay beyond.
“Where did you ask Cosmos to take us?” asked George.
“I told him”—Annie was now speaking through the voice transmitter in her space helmet—“to take us to see water in space.”
George and the Unbreakable Code Page 7
