Previously on: Part 2: Memory Uncovered, Bus Uncovered
Where we left off last time, Alfy wakes up from chaos and accidentally finds that his brain is stored in a computer memory by data. Alfy wants to escape from here, but the memory tells him that if he doesn’t store himself persistently soon, he will disappear once the computer is shut down. Below memory help, alfy finally came to hard disk.
The third: data what depend on, hard disk talk principle
Suddenly, a huge thing flew from the distance, not far from the head of the alfy in the place quickly skimming, scared alfy subconscious flash.
Alfy has no time to see, the thing has gone.
In the time that followed, it appeared at intervals, so regularly that, over time, it became normal.
Alfy began to take a close look at the new place. The direction above was dark except for a brief moment of light when the thing appeared. And at the foot of the direction, Alfy found countless small particles in turn, from near to far, can not see to the end, a bit like the memory of the orderly arrangement of capacitor units, careful but completely different.
“What are these little particles? “Whispered Alfy.
“The new person is not clear, that is the metal magnetic particle”, nearby, someone with him on the conversation.
“Who’s talking?
“I’m a file in the sector next to yours,” the voice said.
“Hello, I did just get here. Did you just say it was a metallic particle? What is a metallic magneto?” “Asked Alfy.
“These are the things that store data on the surface of a mechanical hard disk. Our data is represented by them. Metal magneto particles are polar, and multiple magneto particles form a cell to represent a bit.
Alfy suddenly realize, “originally be so, no wonder before the hard disk again call disk”, then ask a way again: “that why is not left and right, but up and down?”
“You’re right, early hard drives used to record data horizontally, but today’s hard drives are used vertically because they use less space, can hold more cells per unit area, and have more storage capacity,” says the next file.
Alfy nodded, originally this mechanical hard disk is such storage data.
“Well, how do you know so much?” “, alfy some curious.
No sooner had he said that than the huge thing passed overhead again.
“What is it? Why is it always hovering over my head?” “Whispered Alfy.
“That’s the head.”
“Head?”
“Yes, the head is the tentacle that reads and writes data to the hard drive.”
“Then how does it get around? And then again, and then again.”
“It’s not flying. It’s the disc that’s spinning under our feet.”
“We’re turning? “Alfy can’t believe it.
“Yes, this hard drive can rotate at 7,200 revolutions per minute!”
“So soon? Why can’t I feel it?”
“The earth is still turning, and humans can’t feel it either,” the document says with a laugh.
Just then, the thing called the magnetic head turned around again, and this time, the magnetic head closer than ever, just over the top of the alfy, this time alfy saw clearly, at the end of the magnetic head, there are two devices, a large and a small.
Soon hit, alfy scared closed his eyes.
“Already left, see frighten you”, the document next door chuckles.
Alfy opened his eyes, that thing as expected had disappeared traces.
“What just happened, I was so close, I thought it was going to hit me, scared me to death,” alfy said.
“Don’t worry, just the magnetic head in reading your data, although the distance is very close, only a few nanometers, but absolutely will not hit, then the hard disk is destroyed.”
“Read my data? Why don’t I feel anything? How does it read?”
“At the end of the head, there are two things, a large one and a small one, a writing head and a reading head, which float a few nanometers above the surface of the disk. As the reading head scans, electromagnetic technology can detect the polarity of the magnetic particles in the lower cell, and it can tell whether it is a zero or a one.”
“Those two things, I just saw, they were read and write heads. The data reading process you’re talking about sounds a bit like the way a phonograph turns the grooves on a record into sound, “alfy said.
“Well, that’s what you mean.”
“I see. How do I write data?” “, alfy cross-examine arrive.
“The write head on the side can change the polarity of the metal particles in the cell by using the magnetic field, setting it to either 1 or 0.”
“Wonderful! “, alfy can not help but sigh to, human is really clever, industrial technology is really powerful, can invent such a delicate thing in such a scale of space.
“How do you know so much? You know everything.”
“Because I’m a PDF, and I’m talking about the Principles of Mechanical Hard Disk Storage, and all of this is in the document.”
“That you say to me again, this hard drive so big, one eye can’t see to the end, how does it know I in which position?”
“Although this hard drive capacity is large, but the above storage location is through uniform address, want to find you easily.”
“Oh, how exactly?”
“Hard disks are stacked on top of each other. The disk surface is a circle, and from the inside out it is divided into many circles, or tracks, and each track is divided into many sectors, or sectors. Hard disks read and write in sectors.
“Alas, wait a minute, since it is a fan, the area of the outer circle is larger than the inner circle, if each sector is fixed to store 512 bytes, the outer circle fan is not a lot of waste of area?” “Asked Alfy.
“You’re thinking fast. Yes, that’s what happened in the early hard drives. Each track had the same number of sectors, which made addressing easier, but you ended up with small sectors in the inner circle with high data density, and large sectors in the outer circle with low data density. But in order to increase the capacity of the hard disk today, we don’t allow this to happen. The number of sectors is no longer the same among the different tracks. The inner circle area is small, the number of sectors is small, and the outer circle area is large, the number of sectors is more.”
Alfy fell into thinking, his mind began to imagine the circle and circle of track.
The file goes on to say: “When reading or writing data, the hard disk driver will calculate which disk surface, track and sector number the data is on. First, the head is moved over the track by the head arm, a process called seeking, and then the data can be read and written by waiting for the corresponding sector to rotate under the head.
“A sector is only 512 bytes, what if more than, like I have more than 20 MB, how do I store?”
“You need to occupy more than one sector. That’s a problem for the file system to solve. I don’t know.”
Just say that finish, that thing again came to alfy directly above.
“Strange, how to read my data again”, alfy some puzzled son.
“Alfy, alfy ~”, thinking, the direction of the head came at the beginning of that mysterious old man’s voice.
“There you are again. What do I have to do to get out of here?” “, alfy anxiously asked.
The old man did not pay attention to alfy’s problem, just calmly said: “You have been found by the anti-virus software, will soon be killed from the hard drive, if that is the case, you will never wake up”
Alfy heart tight, thought to come to hard disk originally safe, had not thought to have not been slow to come, be targeted by anti-virus software again, more can be angry is oneself be regarded as a virus actually.
“What should I do? Tell me.”
“Hide,” the old man said.
“Hide? How?”
This time, alfy did not wait to answer, the old man once again disappeared without trace.
Want to know the follow-up, welcome to leave a message to share forwarding, like broken 100, open more next time: the story of the file system
Series of review
“Second: Memory uncovered mystery, bus solution machine”
1. Genius in Secret, Jedi in Search of Life