“You will get to see some of the System yourself, on the way to the CPU,” he told Billy, “And I think you are in for a few surprises. I have seen most of it, but new things keep appearing all the time, and I have to keep learning how to deal with different messages for different Components.”
“What are ‘Components’,” asked Billy, rather hesitantly, as he was very impressed by Monty’s wide range of knowledge, and did not want to appear too ignorant. He need not have worried about being patronised by Monty, however, as Monty was obviously delighted to be able to pass on information, without making Billy feel at all silly for asking.
“Components are the parts of the System,” explained Monty, “For example, you live in the Memory Component, where the CPU stores information that has to be remembered, but is not needed right at the moment. The information, or data as most of us call it, is kept in Memory by the CPU using you and the other Bits in groups called Bytes.”
“I see,” said Billy thoughtfully, “So Mr. Write tells us the information, and Mr.Read collects it whenever the CPU needs it again.”
“That’s it!” returned Monty, clapping Billy on the back, “You’ve got the idea straight away. What an intelligent Bit you are, to be sure!”
Feeling very pleased with himself at being called ‘intelligent’, Billy asked about other Components, and Monty started to list them on his fingers. As there were of course eight on each hand, he only needed one hand for those which he declared were the most important:
“Number One,” said Monty, “Is the CPU - the overall boss of everything. Makes all the decisions, controls the movement of data around the system, and tells all the other components what to do and when to do it.”
“That sounds like a hard job”, responded Billy, “The CPU must be very, very clever!”
“Oh definitely!” said Monty, “’Though there is a Mathematical Unit to help with some of the arithmetic when the CPU is busy, so I suppose you could call him Number Two. Then of course, at Number Three, must be you chaps in Memory.”
Billy had not realised how high he and his friends would be on Monty’s list, and was quite pleased to hear that they were quite important. He did, however, start to get a vague feeling about why his behaviour caused such an upset. But what Monty was telling him was far more interesting, so he pushed the feeling to the back of his mind, and asked Monty to carry on.
“At Numbers Four and Five and Six,” Monty continued, “I would think could be the Input/Output Components, for there would not be much point in the System being so clever if humans could not ask questions and receive answers. They use the Keyboard and a thing called a Mouse to send some of their requests to the System, and a Monitor to display the answers. By the way, did you know that when they use the Keyboard, they only have ten fingers to press the keys? I really don’t know how they manage.”
The news about human’s fingers sounded very strange to Billy, but he was more interested in hearing in the rest of Monty’s list.
“Well, at Seven and Eight”, said Monty, “I suppose you would include the Hard Disk and the CD ROM. He paused for a moment, and then said, “But that’s enough from me about the System Components for now. It will be better to tell you more when you actually get to see some of them.”
Monty was obviously starting to get tired of sounding like a teacher, so Billy did not ask any more questions for a while, but as they continued walking, Billy pondered on what he had heard. If there was a Hard Disk, he reasoned with himself, did that mean there was also a ‘soft’ one? And what on earth could a CD ROM be? Really, things were getting far more exciting than he had ever hoped.
Now that he was not looking at Monty all the time, Billy started to notice just how many parts there were in the Memory area. The rows of Bytes stretched to each side and behind him for as far as he could see. He realised that the stories he had heard about ‘Kilo-Bytes’ and ‘Mega-Bytes’ might be true, so he risked asking Monty another question, enquiring what the words meant. Now that a different topic had been found, Monty became quite chatty again:
“That’s easy,” he said, “Kilo just means ‘a thousand’, and Mega means ‘a million’. In our System we have two hundred and fifty six Mega-Bytes of Memory”, he added proudly.
“Wow!” exclaimed Billy, “That sounds like an awful lot. But why exactly two hundred and fifty six, why not two hundred and fifty five or two hundred and fifty seven?”
“Because two hundred and fifty six is exactly sixteen times sixteen, Silly!” retorted Monty, “You know we do nearly everything in multiples of sixteen here, or certainly in two’s. Odd numbers don’t get much of a look in.”
“Ah! Yes, of course,” said Billy hastily, trying to cover his slip. “It’s quite clear, really.” But he was still really a bit puzzled, and continued, “But you just talked about thousands and millions, and if I have got it right, you can’t divide them by sixteen and get a whole number.”
“Good point, well made!” responded Monty. “But when we talk about Kilo’s, we really mean one thousand and twenty four (1,024), which can be divided exactly by sixteen. It’s the same with Mega - that means one million, forty-eight thousand, five-hundred and seventy-six (1,048,576). It’s just easier to say Kilo and Mega - but you’ve done well to spot that point, some never quite grasp it.”
Billy felt better after this exchange, for he was keen to show that he did understand what Monty was telling him.
“I say!” he commented, still quite pleased to be able to change the subject, “We seem to have come to the end of the Memory area.”
They had, indeed, reached the end of the rows and rows of Memory. Now that he could look sideways without interruption, Billy saw that they were now near the lights he had earlier only seen in the distance, and they were illuminating a wide and flat area, with lots of metal bars running side-by-side to the right and to the left. As he looked in each direction it seemed as though the bars all joined together at a point in the distance, so he realised that they must stretch for a very long way. He noticed that the data line that they had been walking along, joined up with some of the bars, and that the lines from other Memory areas did the same. It looked like the drawing of lots of giant noughts-and-crosses games, just before anyone had started putting in the noughts or crosses, and Billy was wide-eyed with surprise at the wonderful sight.
“Here we are!” declared Monty, “At the System Bus!”
Chapter 3 The Main Road
“Now you mustn’t think that this is what humans call a ‘bus’ – that’s short for omni-bus, which is used for carrying lots of people from place to place. It’s a totally different thing,” said Monty, as Billy stared at the vast array of metalwork in front of them. “The ‘bus’ in System Bus is short for ‘busbars’,” continued Monty, “But instead of carrying electricity, these bars carry information quickly around the system, to and from the CPU and the other important Components. It’s like a super-fast data highway.”
Billy vaguely recalled hearing that a highway was something that humans used to travel from place to place at high speed, so he started to get some idea of what Monty was talking about.
“This System,” added Monty, “Has thirty-two bars on the System Bus, but some of the earlier systems had only sixteen or even as few as eight. However, they are considered very old-fashioned now. Ours can address millions of individual Bytes, and carry data from four Bytes all at once,” he declared with a flourish.
“But where’s the data?” asked Billy, for all the bars that he could see were quite empty.
“Wait for a moment,” said Monty, patiently, “And it will all become clear.”
Just then a very strange contraption appeared. If Billy had known what a bicycle was, he might have thought it was something similar, but it had thirty-two wheels instead of just two. The other difference was that the wheels were mounted in a frame so that they were side-by-side, instead of one behind the other. The wheels had s
haped metal rims that fitted over the top of the bars on the System Bus so that they could not come off, and each wheel ran on one of thirty-two bars.
“Whatever can that be?” asked the astonished Billy.
“Why it’s a Clock Cycle,” responded Monty. “They’re used to carry the data around the Bus.”
As he looked closer, Billy could see little figures sitting on the frames, one above each wheel. Their feet were on pedals attached to the axles of the wheels, and their legs pumped up and down furiously as they propelled their strange vehicle along the bus. Bill noticed that their legs were all exactly in time with each other, and that they were dressed in suits made of a very shiny material. They also wore strange swept-back hats on their heads. When he commented on these points to Monty, he received the following explanation.
“They have to be synchronised,” said Monty, “That is, all moving together, to ensure that all the data arrives at the same time, and there are no mix-ups. It takes lots of training to be able to do that, and they have to be very fit and strong. Their clothes are made out of a shiny material, called ‘Lycra’ I think, which is some new stuff that they have just started to wear. It helps them to move fast by cutting down wind resistance. The funny shaped hats are worn for the same reason. You have probably already guessed that the speed at which the Clock Cycles go round the Bus determines how quickly the CPU can move information backwards and forwards, so the faster the better.”
“You see those boxes on the frames behind the riders?” continued Monty, “One contains Addresses and the other Data. When the Clock Cycle reaches a specific place that matches the address in the Address boxes, information is taken from, or put into the Data boxes, depending on the instructions given by the CPU. Each of the big Components has its own address, but the Memory area has lots and lots of addresses because it has to store so much information.”
Just then, the Clock Cycle slowed to an abrupt stop, right beside the data line that ran from the row in which Billy’s home Byte was situated. Almost knocking Billy over as he went past, Mr. Write suddenly appeared and he rushed up the line, and ran quickly across the Bus bars, gathering bits of paper from each of the Address and Data boxes on the Clock Cycle on the way. If Billy had ever seen an American footballer in training, stepping quickly in and out of rows of old car tyres whilst trying not to trip, he would have recognised the way that Mr. Write moved so quickly without falling over. The only things missing were the large helmet and the wide, padded shoulders! When he reached the furthest bar, and had collected the last piece of paper, Mr. Write turned round and reversed his jerky progression across the Bus, finally disappearing behind Billy and Monty as he rushed back up the data line.
“The information in the address boxes tells Mr. Write exactly which four Bytes are to receive the data he has to deliver,” explained Monty, “But it’s just by chance that it happened to be your Mr. Write that we saw. There is of course, a Mr. Write and a Mr. Read for every row of Memory.”
As Billy turned to watch Mr. Write go, he noticed that there were address signs at the end of each row of Memory, and Monty confirmed that they were there to help the Clock Cycles know where to stop. As he turned back, Billy saw that the Clock Cycle was already zooming off, with thirty-two sets of legs pumping up and down at a furious rate as the riders drove their strange machine into the distance.
“I suppose that when the CPU wants to get some data that Mr. Write stored previously, Mr. Read takes over from Mr. Write,” said Billy.
“Yes, that’s true,” said Monty, “But he has to make a double trip. He collects the correct address information from the Clock Cycle first, then he has to rush off and get the information from the Bytes before he can come back and put it into the appropriate data boxes.”
“I never realised before what demanding jobs Mr. Write and Mr. Read have,” said Billy, “I’m sure that if I tried to run across the Bus at the speed that they do, I’d be certain to fall flat on my face! They must have to watch the System Bus very closely to see if any Clock Cycles have any work for them.”
“Well, it’s time we were on our way to the CPU,” declared Monty. “We shall have to hitch a ride on the next Clock Cycle that comes past.”
“How will we get one to halt?” enquired Billy, “Unless we happen to be near where one stops, like just now, they are moving too fast for us to be able to jump on!”
“That’s easy,” advised Monty, “We just use an “IRQ.”
“Oh! The Interrupt ReQuest that Mr. Read mentioned, said Billy. “Where do we get one of those?”
“We Mail Messengers have our own,” replied Monty, delving into one of his pockets. He took out a small cylinder and tapped it smartly on the floor. This caused the cylinder to expand into a long rod. Monty took a piece of red cloth, like a large handkerchief, from another pocket, and attached it to a clip on one end of the rod.
“There we are!” said Monty. “One do-it-yourself IRQ.”
Monty then stood beside the System Bus, and waved the IRQ vigorously as another Clock Cycle came into sight. Just when Billy thought that it would speed past them, it screeched to a halt beside Monty.
“Where to?” enquired the nearest rider, who did not seem at all out of breath despite his exertions. He was wearing a yellow armband with ‘MSB’ written on it, and Billy later learned that ‘MSB’ meant ‘Most Significant Bit’, which was something to do with how addresses are organised. For the moment though, Billy was more concerned with the next stage of his journey.
“CPU, please,” responded Monty, which brought a look of respect from the riders who heard his reply, but Monty took no notice, for he had made the trip many times before. He closed up his IRQ rod, and put it and the red flag away in his pocket. He then indicated to Billy that he should sit across the boxes behind the next rider, whilst Monty himself sat on the ones behind the rider with the armband. Billy hopped across the first System Bus bar, and sat himself on the boxes, which luckily had flat tops so were fairly comfortable.
“Hold tight! We’re off!” cried the armband wearer, and all of the riders pushed down on their pedals at once, accelerating the Clock Cycle to high speed very quickly, giving Billy the feeling that he had left his stomach floating in the air at the place that they had just left.
Chapter 4 Sightseeing
At first, as the Clock Cycle whizzed along, Billy was a bit frightened (or a frightened Bit, if you like), and thought that he was going to fall, and suffer some terrible injury. Also, the rush of air made his eyes run with tears, so he was most uncomfortable, and wished that he was back in his safe, warm hole in the Memory area. After a while, though, he began to see that as the bus bars were so straight and flat, there was little chance of him being shaken off. He started to calm down a little, and relaxed his tight clutch on the frame. He noticed that this caused his knuckles to return to their normal colour - they had previously gone almost white with the tension of his frenzied grip! He looked across at Monty, who was obviously totally unaffected by the experience, and was sitting quite nonchalantly, not even holding on at all. Billy realised that they were quite safe whilst the cycle ran at speed, for it was only during starting and stopping that one would need to hold on. For this reason, he hoped that he would get some warning before they started to slow down. In case a warning did not come, and because he wanted to be safe rather than sorry, he kept both his hands resting lightly on the frame, ready to grab it tightly if necessary. It was well that he did, for just as he had worked all this out in his mind, the track made a sudden, sharp turn to the right. They raced around the bend without slackening speed at all, and because Billy’s side of the cycle was on the outside, it went even faster than the other end. As Billy was well prepared, however, he only had to hold on tightly for a few moments, and lean over a little to keep his balance.
Now that he was more at ease, Billy began to take notice of the new view that was presented to him after the turn. They were
passing over a set of data lines that went from the System Bus to a low, flat-topped building on the right-hand side of the track. This had a long bendy flat ribbon going from the roof, and right up high into the air until it disappeared from sight. He noticed that the ribbon was made up of about eight or nine separate strands, all joined together side-by side. Running up and down the strands were little creatures, each of which had a little bag slung over his shoulder. Pointing at the building and its ribbon, Billy called across to Monty to find out what they were.
“That’s an Input-Output Port,” shouted Monty. “I mentioned them when I told you about the System Components. This one is for the Keyboard, and that smaller one behind it is the Mouse Port. Those ‘ribbons’, as you called them, are actually called cables, and they go all the way out of the System to the Keyboard and Mouse.”
Billy had not spotted the smaller building until Monty mentioned it, but now saw that it was much the same as the larger one, only it had a smaller cable. He also noticed that the creatures on the smaller cable were dressed differently to those on the larger one.