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Nomake Wan
Posted: Jan 12 2018, 01:31 AM


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QUOTE (umustwait101 @ 28 seconds ago)
I feel like the more we discuss this, the more we find out that when it comes down to the concrete details, we agree on many things, and where we differ is where we feel whether those concrete details have a tangible impact.

The problem is that you refuse to recant your stance that the mere act of reading data degrades the data (false), and that hard drives have a superparamagnetic limit so low that they flip bits at room temperature (you have provided zero evidence for this claim). So no matter how long we go back and forth on this, until you finally give up these nonsensical claims there will never be any agreement.

QUOTE (umustwait101 @ 28 seconds ago)
One thing I wish to point out, however, is that the shielding is not intended to block the magnetic field from the read element from impacting the data; it's to actually block ambient magnetic fields from increasing the noise so that the signal will be stronger.  Unfortunately, while it may not have been good enough for me to have just noticed there were permanent magnets on the read element clearly labeled as such, and to have decided it was good enough, there are, nonetheless, permanent magnets pointed in the same orientation as the data (parallel, if you will).  Paper 8, from my previous link, in figure 2, there are three interesting lines of note, on the right side: the "signal magnetic field", the "free layer", and the "pinned layer".  Under section 2, we get a basic understanding of the mechanics behind how the read head works: the magnetic free layer is affected by the signal magnetic field, and depending on whether the free layer's magnetization is parallel or antiparallel with the pinned layer, that causes a difference in resistance which registers as the value of the data.  Thus, we already have a hint here, that there is a permanent magnet in the system; otherwise, there would be no reference with which to compare the signal with.  After further digging, we discover under section 3.3, that the pinned layer is most likely a permanent magnet (a ferrimagnet).  This is only indirect, because they did not say explicitly that the material they used was a ferrimagnet, but that they used one type of material, while acknowledging that another similar material was used as the ferrimagnet material.  I hope it isn't considered too much of a stretch to say that they simply used an alternative ferrimagnet material with a slightly different chemical composition.  And with that, this should be conclusive proof that there is indeed a permanent magnet in the hard drive head that is oriented in such a way as to be able to affect the data simply from reading.

The 'round in the chamber' I've had ready and raring to go just in case you did something silly like refuse to give this nonsense up is in fact the PMR paper from HGST that you had posted earlier. I had already used part of it to counter your claims in the earlier post, but after making that post I read past the part I needed to do that and realized that the remainder of that paper completely blows your theories out of the water.

QUOTE (HGST)
The unique feature seen in the perpendicular system is the “soft magnetic underlayer” incorporated into the disk. This underlayer conducts magnetic flux very readily. When the write head is energized, flux concentrates under the small pole-tip and generates an intense magnetic field in the short gap between the poletip and soft underlayer. The recording layer that stores the data is directly in this gap where the field is most intense. Higher fields allow “higher coercivity” media to be used. Such media require higher fields to set the magnetization, but once set, the magnetization is inherently more stable.

Here, there are some important points to unpack. First, note the obvious--that a write head is an electromagnetic construct. This should have been obvious because how else are you controlling what's actually written, but since you seem to think that magnets just kind of exist as part of the writing process itself, let's get that out of the way with this paragraph (and its associated diagrams of both LMR and PMR heads, both of which are clearly electromagnets as shown by the coil and voltage applied).

Second, note the part about coercivity of materials. I actually brought this up quite a while ago--when superparamagnetic limits were first introduced to the discussion--and it's a critical point to remember. The rest of the paper goes into some awesome details about write-head design, like how the trapezoidal shape and trailing shield is designed specifically to sharpen the fields and, I quote, "Fabricating a narrow trapezoidal pole with a well-controlled bevel angle is essential to prevent the fields from the pole surface erasing data in neighboring tracks." The sheer number of times HGST takes pains to point out the essential mechanisms to prevent data from being altered inadvertently should clue you in to how insane your claims are. If you read the paper in its entirety that should be enough to change someone's mind... but since previous posts still haven't managed to dissuade you, let's get nitty-gritty into some materials science.

So, if you're going to argue about magnetic data being altered, what you're talking about is intrinsically linked to two concepts of materials science. These concepts are coercivity (we talked about this earlier--this is how 'easy' it is to get a material's magnetic structure to change at a given temperature) and the oersted (Oe) rating of a magnetic field (magnetic field strength). In paper 8, which you yet again try to use as your 'a-ha!' moment, you'll notice that Fujitsu actually helpfully gives a rough Oe rating for the materials in the read head (though, likely for proprietary concerns, they don't give a precise number. These can be found around section 4, namely the part where they mention being over 1000 Oe. I found a Korean paper which came to a similar conclusion (High Exchange Coupling Field and Thermal Stability ofAntiferromagnetic Alloy NiMn Spin Valve Films (WARNING: PDF DOWNLOAD)). In this paper from 2000, they achieve 650 Oe from their pinning layer, and note that an Oe greater than 300 Oe is required for proper spin-valve operation. Keep those numbers in mind, because now we move on to the platter material. Remember that coercivity thing from earlier? Well, wouldn't you be curious as to just how many Oe it takes for the write head to make a change to these new media? Me too! Let's find out!

Remember the PMR paper from HGST, and how it mentioned that increasing the coercivity of platter material was critical to reducing bit size and increasing density without sacrificing stability of the platter's magnetic properties? Well, here's another reference to that (clicky!), pointing out the importance of superparamagnetic limits, and then referencing research into platter materials with coercivity in the 30,000 (!!) Oe range. However, I couldn't find any evidence for existing platters which have such high coercivity, so instead here's a bunch where the actual values are shown:

Materials Today, Carnegie Melon University
QUOTE (Article)
To achieve the optimum transition sharpness, the field magnitude needs to be optimized such that its gradient at the center of the transition is a maximum. This means that the maximum write head field in the medium has to be approximately twice the coercivity. The field generated by a write head is determined by the magnetic flux density inside the head poles at the gap. In current HDDs, the maximum head field is slightly less than half the magnetic flux density in the head poles. Over the years, the head pole material in the gap region has changed from permalloy (Ni81Fe19) with saturation flux density Bs = 1.0 T, to Ni45Fe55 with Bs = 1.5 T, to Fe65Co35 alloy with Bs = 2.45 T, which is used in write heads manufactured today5-7. At the same time, the coercivity of thin film recording media has increased from 2000 Oe to 4800 Oe. However, the alloy Fe65Co35 used in today’s write heads has the highest saturation magnetic flux density (Bs = 2.45 T) of any existing magnetic material.
QUOTE (Article)
According to the NSA, current hard disk drives have a coercivity of up to 5,000 Oersteds and tapes have up to 3,000 Oersteds. In order to ensure complete erasure they need to be exposed to a strong magnetic field. A general rule of thumb is a Gauss force of at least 3 times the media’s coercivity. So a 5,000 Oersted hard drive would require 15,000 Gauss (1.5 Tesla) which a reputable degausser can produce. Of course, along with the data, prerecorded factory information like the servo tracks are also erased which will render the device unusable, which is the goal.

In case you were curious about the NSA data, it's from HERE, on page 14.

So, in short, the more dense a drive gets, the higher the coercivity of the media needs to be in order to store bits that small. The higher the coercivity of the material, the more Oe it requires to cause the magnetic data to change. As a result, the limiting factor in these materials is actually the Oe output capability of the write head. Without a suitably powerful magnetic flux, that data isn't going anywhere. That's the whole idea. So I'm sorry, Umu, but you are just plain wrong. The more dense we get, the more reliable the magnetic data becomes!

QUOTE (umustwait101 @ 28 seconds ago)
Very valid and astute observation.  I indeed did take things too far with this one.  My point is that the increase in density trumps data retention, as long as they can maintain the "industry-standard data retention expectations".  While "industry-standard" sounds good, it's basically an alternative term for "what everyone else is doing".  Well, everyone else could be designing drives to only retain their data for a year, and that would be considered "industry standard", and there's no proof that they aren't doing just that.  It's actually pretty smart, because they don't have to prove anything; they just have to say that they do it just like anyone else, so you don't really have any better choice by going with their competitors.  And they all do that.  MTBF isn't proven; it just uses an "industry-standard" methodology of determining the number.  It is useful in allowing consumers to compare apples to apples, but it doesn't really accurately predict the longevity of a hard drive.  But, I digress..

No. You have yet again attempted to dodge the need to provide evidence by ignoring the fact that you are the one who made the claim. If you claim that "industry-standard data retention" means "drives with superparamagnetic limits so low that bits flip at room temperature," the onus is on you to prove that that is the case, not on me to prove that it is not. If you truly, honestly believe that every hard drive manufacturer on the planet is so completely oblivious to that which they go into painstaking detail about in these white papers, then I will ask you one more time. Provide your evidence for this claim, or drop it.

...Oh wait, I already disproved it earlier with the coercivity thing. Whoops.
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APX
Posted: Jan 12 2018, 04:19 PM


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QUOTE (Sensation! @ Jan 9 2018, 11:44 PM)
A late response, but relevant

http://i.imgur.com/vClcpLX.jpg

First week in, he never mentions a calculator, but that's because he's a chill af and great professor.

Also the college lends out calculators, so I got me a TI-84 Plus for the semester, free!

So far I have picked out some pretty damn good professors (Also due to looking at ratemyprofessor)
Sensation!
Posted: Jan 13 2018, 02:02 AM


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QUOTE (APX @ 9 hours, 42 minutes ago)


Also the college lends out calculators, so I got me a TI-84 Plus for the semester, free!

Bro...fuck yeah!
I had to buy one back in HS :/
Nerubian
Posted: Jan 14 2018, 07:39 AM


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xiao
Posted: Yesterday, 2:12 AM


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Can you believe that IDW has outlasted TechTV, AOL/AIM, and MySpace ~ also it's older than the iPhone, YouTube, and Revenge of the Sith ..

Just something that dawned on me while I was taking a jog earlier & it kind of blew my mind user posted image

SPOILER
Nomake Wan
Posted: Yesterday, 11:06 AM


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Yeah, it's hard to believe that I joined IDW back in high school and now I'm a salaryman. What impresses me even more is the age of the code that runs IDW. It's a true testament to Perry that we've been able to survive so long on this old version of IPB without any major issues and without security problems.

In completely unrelated news, I really hate "UPS Innovations" shipping. It's nonsense. The idea is UPS handles a shipment until it reaches the general area of the recipient, at which point it joins a huge pallet of other UPS Innovations mail which is sent to a USPS processing center. The pallet then has to be broken down, the mail sorted, and then sent to the proper post office before final delivery. What all this means is that your package can be within an hour of your house and yet it will take three full days to travel that one hour driving distance.

And there's nothing you can do about it. Fuckin' worst.
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xiao
Posted: Yesterday, 4:16 PM


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QUOTE (Nomake Wan @ 5 hours, 2 minutes ago)
In completely unrelated news, I really hate "UPS Innovations" shipping. It's nonsense. The idea is UPS handles a shipment until it reaches the general area of the recipient, at which point it joins a huge pallet of other UPS Innovations mail which is sent to a USPS processing center. The pallet then has to be broken down, the mail sorted, and then sent to the proper post office before final delivery. What all this means is that your package can be within an hour of your house and yet it will take three full days to travel that one hour driving distance.

And there's nothing you can do about it. Fuckin' worst.

Yeah when I've dealt with direct UPS/FedEx/DHL .. if it's straight to my house with no "Innovation" BS it's pretty darn fast ~ but I've never used that new Innovations thing.

I'm pretty good at tracking what I've ordered ~ and a couple of times I've gone to my local USPS Post Office & since I'm friends with the guys .. I just showed them my ID with my address on it, and they signed me off & gave me the shipment.

Usually I just walk up to the front-desk, but some other times I've just gone thru the back & asked one of the carriers if they had the package. I showed them my ID and they verified by calling my phone ~ so they gave me the shipment by walking up to them.

Recipients shouldn't have to do that .. but jumping thru circus hoops seems to be the SOPMO of any kind of delivery. I particularly dislike USORDA in Chicago (a customs sorting center) ~ they poke butt & delay my international shipment by half a week sometimes. Not to mention I can't get an f'ing Tokyo Marui w/o painting the nose of the proplica fugly Naruto orange or yellow :V pacman ~

... ... ...

In semi-related shipping news ~ Avex didn't stop w/ prohibiting Super Eurobeat & Kamen Rider merch via CD Japan .. they've straight-up gone & banned their K-pop groups like EXO from shipping outside thru CD Japan. But Amazon JP is still cool tho' huh.gif ~ so it makes me wonder if Avex just really hates CD Japan/NeoWing™ or if they're selectively just shooting themselves in the foot .. or if CD Japan is just a bunch of lying butt chickens that don't feel like shipping certain products outside of Nippon .. w3rd ~ maybe Avex has a contract with Amazon Japan ~ the world may never know

SPOILER
APX
Posted: Yesterday, 5:41 PM


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YOUTUBE ( https://www.youtube.com/watch?v=sGTqmgFYYNI )


I have to admit...

SPOILER
kyonpalm
Posted: Yesterday, 6:33 PM


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Indeed I feel older every time I visit here. And this year will be my 10th. Fuck.
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xiao
Posted: Yesterday, 8:01 PM


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We're like the perfect middle between the Something Aweful and RX7Club forums & still manage to keep this site ~ somewhat family friendly ..

Our little baby Initial D anime is gonna be 20 y/o this April 18 user posted image

[ Post made via Mobile Device ]
kyonpalm
Posted: Yesterday, 8:29 PM


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QUOTE (xiao @ 27 minutes, 51 seconds ago)
Our little baby Initial D anime is gonna be 20 y/o this April 18 http://idforums.net/style_images/1/icon12.gif

Somehow, it freaks me out more to think that Initial D was only 7 years old at the time I got into it than that it's 20 years old this year.
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xiao
Posted: 8 hours, 16 minutes ago


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QUOTE (kyonpalm @ 4 hours, 12 minutes ago)
Somehow, it freaks me out more to think that Initial D was only 7 years old at the time I got into it than that it's 20 years old this year.

I still remember going to Hollywood Video around 2003 ~ looking at the hot picks DVD's wall ~ seeing the Tricked Out version ~ and going 'oh hey!a Fast & Furious anime !!' .. and here we are 15 years later laugh.gif
Nerubian
Posted: 2 hours, 17 minutes ago


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Well, it will be my 7th year in a few days already. That's a horrible thought.

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