Posted on 02/16/2012 8:16:39 PM PST by neverdem
An ultrashort heat pulse can predictably flip a bit in a magnetic memory like the one in your hard drive. The surprising effect could ultimately lead to magnetic memories hundreds of times faster and more energy efficient than today's hard drives. It also provides a way to control the direction in which a bit is magnetized without applying something else that has a direction, such as a magnetic field.
Two decades ago you could boast that your new desktop computer had a hard drive that could hold 20 megabytes, or 160 million bits, of information. Now, laptops come with disks as big as 1 terabyte—a 50,000-fold increase in capacity. But larger storage capacity must go hand in hand with the ability to read and write bits faster.
Each bit in a magnetic recording medium is in fact a nanometer-sized patch or "domain" that can be magnetized in either of two directions—say, up and down—to encode a 0 or a 1. That information is read out by the read head, a tiny electromagnet that passes over the rotating disk and measures each domain's orientation. The same head also writes the information to the disk by applying a magnetic field that flips a bit's orientation. But the traditional electromagnetic read head struggles to keep up. For a while now, the time needed to write one bit has been stuck at about 1 nanosecond, limiting the rate of data transfer.
That's one reason researchers are searching for much faster ways to flip magnetic bits. One possibility is to heat up the magnetic domain while applying the magnetic field, making the bit easier to flip. But now Alexey Kimel, a physicist at Radboud University Nijmegen in the Netherlands, and colleagues have found that heat alone might do the trick. An ultrashort laser pulse causes a rise in temperature that in a couple of thousandths of a nanosecond controllably switches the orientation of the magnetization of an alloy of gadolinium and iron, the researchers report today in Nature Communications.
The odd thing is that the heat pulse has no direction to tell a tiny magnetic domain which way to point. So at first blush, it might seem like a heat pulse alone should produce a random result, sometimes flipping the bit and sometimes not. Instead, the heat pulses flipped the bit back and forth like a light switch with complete predictability. "This was a total surprise to us all," Kimel says.
The key effect lies in the atomic-scale details of the material—in this case iron and gadolinium—placed on alternating sites in a regular pattern called a crystal lattice. Each atom has its own magnetism. In the material, the iron and gadolinium atoms are magnetized in opposite directions. Because gadolinium is more magnetic, the "ferrimagnetic" material as a whole is magnetized in the direction of the gadolinium atoms. If the material were heated slowly, the interaction between atoms would no longer be able to keep all the spins neatly aligned, and the magnetic order would disappear in a process somewhat like the melting of a solid, Kimel says.
But in the current experiment, laser light heats up the gadolinium-iron alloy so incredibly fast—in 1/10,000 of a nanosecond—that at first only the iron atoms lose their mass orientation. The gadolinium atoms react more slowly in losing their magnetization. And once the iron atoms get hot enough and are free to pivot around, they prefer to align in the same direction as the gadolinium atoms. Then, as the material quickly cools and the orientations of the atoms freeze up, the iron and gadolinium atoms again prefer to point in opposite directions. But this time, it's the slow-cooling gadoliniums that flip leading to a predictable overall reversal in the material's magnetization. "We do not understand the full details of this mechanism yet," says Thomas Ostler of the University of York in the United Kingdom, who performed calculations on the ferrimagnetic material.
The observed effect could make magnetic recording media like hard drives hundreds of times faster. "Writing bits this way is potentially much more energy efficient, because there is no longer a need for energy-consuming electromagnets," Kimel says.
Of course, the new technique must compete against others. In recent years, researchers have shown that they can flip magnetic bits with oscillating electric fields or currents of electrons all spinning the same way—strategies that involve physical entities with directions.
"These techniques will probably be used in commercial products sooner, because scientists and engineers have already been working on them for a couple of years," says physicist Bert Koopmans of Eindhoven University of Technology in the Netherlands, who was not involved in the research. "Personally, I don't see this laser-induced bit switching incorporated in hard drives any time soon, since the necessary laser systems are now still 1-meter long and hard to integrate." Still, Koopmans says, the new technique may find niche applications, such as ultrafast buffer memories, meant to store information in applications that use fast, optical signals, for which speed is more important than miniaturization.
Ever see one of these? I bought on Ebay for no real reason and it sort of still works. I’m just about out of tape for it. A cleaner view is included as a stock footage clip that I hope someone will buy someday. I have had clips that have sat for a couple of years before anyone used them and this may be no exception.
http://www.youtube.com/watch?v=30x3vJz7Js8
We did it 30 years ago. There were four of them, and it boosted the speed 4X over a single one. But, even mainframe disk devices were really slow back then.
However, it's expensive. And you can accomplish the same thing with RAID-0 and multiple drives. A properly implemented RAID driver will read all the drives in parallel and assemble the results into a single data stream. Of course, each disk device has to be on independent SATA/SCSI/IDE channels.
The truth is that for most people, the seek and rotational latency is what really limits throughput. Seek latency is waiting for the head to move into position, and averages around 9 milliseconds. Rotational latency is waiting for the disk to spin into position, and averages 4.2 milliseconds for a 7200 RPM drive.
Compare that to how long it takes to actually move data. Drives with the latest SATA 6.0 Gbit/sec interface can sustain about 150 MByte/sec, but that is limited by the density of the bits on the drive platter.
The cluster size on your Windows NTFS file system isn't any larger than 32 kilobytes, and is likely smaller than that. Both the operating system and the disk drive do some read-ahead caching and will read more than you request at one time, but let's use 32K as an example. At a rate of 150 MByte/sec, a 32 KByte transfer would require only about 200 microseconds, or about 20 times the average rotational latency. You would have to read about 630 KBytes at one time to just split the average rotational latency time and transfer time 50/50, and that's not even considering the seek latency.
Are you seeing the problem? Very few people read a huge amount of data at one time, repeatedly, and would benefit from a faster sustained transfer rate. And those that do can construct a RAID array much cheaper.
Small random reads are much more common, especially on a computer with a virtual memory system. And that's why operating systems cache disk data in unused RAM, and even individual disks read-ahead and store data in their own internal cache RAM (which are about 32 MBytes these days). When you request that data, it gives you the cached copy instead, avoiding the seek and rotational latency delays.
Well, then its the seek time that is the problem and the value of the achievement this article announces is not what they claim. So do reduce seek time maybe the strategy should be to increase number of platters, decrease platter diameter, drastically increase the power of the hard drive motor, and dramatically increase the hard drive’s on board cache...or go the route of the hybrid SSD.
Thanks for the information/lesson. I honestly enjoyed reading it.
You're welcome. I developed a disk driver many years ago, and always marvel at how far we have come in 3 decades. The magnitude of the numbers have changed, but the mechanical limitations are still the same.
To give you an idea of how much has changed, consider a typical consumer disk drive today: either a 3-1/2 inch desktop drive or a 2-1/2 inch laptop drive. The drive has its own cache and the drive controller circuitry built in. You can buy a moderate size drive for under $100, and hold it in one hand.
Back when I was doing disk driver development, the disk alone was about the size of a dishwasher. The disk controller (for up to 8 disks) was the size of a small kitchen refrigerator. And the cache memory was the size of a minivan (disk cache memory was rare in those days, though).
It isn't just disk storage technology that has advanced so far. Back then, a "scientific" mainframe was distinguished from a "data processing" mainframe by its ability to do floating point operations more quickly. If you were to run the same benchmarks on today's computers, you'd find that your iPhone is 20-50 times faster than the top-of-the-line scientific mainframes back then.
From what I read, it would be an improvement in sustained transfer rate, but I think the real benefit would be the increase in bit density. You would be able to cram more bits on the same sized platter, without increasing rotational speed. As usual, a journalist doesn't quite grasp the significance. :-)
So do reduce seek time maybe the strategy should be to increase number of platters, decrease platter diameter, drastically increase the power of the hard drive motor,
Decreasing the platter diameter would decrease seek time, but you would run into the bit density problem. Ditto with increasing the RPM -- it's already as high as 15,000 RPM for server drives. As the article points out, it takes time to flip a bit magnetically, and speeding up the platter just spreads out the bits. However, all of these things are expensive solutions, compared to alternatives.
and dramatically increase the hard drive’s on board cache...or go the route of the hybrid SSD.
I think that's where we should be going, and I'm surprised that we haven't seen more hybrid SSD's. There are a few, but they are limited in cache size, or are a completely new module, like this one:
http://www.engadget.com/2011/09/01/ocz-revodrive-hybrid-merges-100gb-ssd-with-1tb-hdd-for-499/
However, there are also laptop drives like this one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822148591
They appear to be a significant improvement in performance, but haven't really taken off. If I were replacing a drive in my laptop, I'd use one -- but I'm constrained to the standard offerings in my company's catalog.
SSD has to be implemented carefully: a single channel SSD is pretty slow to write. The good devices organize multiple SSDs into dual, quad, or even octo-channel configurations, in order to be able to sustain the kind of data rate you can currently get with a rotating disk device.
If you are using Windows 7 (and to some extent, Windows Vista), you can implement an SSD cache on your system. Get a fast USB thumbdrive, preferably USB 3.0 (both the device and your system). After formatting, right-click on the drive letter and enable "Ready Boost".
Windows 7 will use the SSD device for short reads. Longer ones will still go to the disk, because it can sustain higher transfer rates. Any writes are written to both the disk and the SSD device, so you can remove the SSD at anytime and your system won't crash. The data on the SSD is also encrypted, so there are no security issues.
If you have an SD card reader built into your laptop, that's an excellent way to use it. Just buy an 8-16G Class 10 memory card, put it in your laptop, and enable ReadyBoost. You can leave it there all the time.
If anyone decides to try this, follow-up and I'll post an explanation of how to use Windows Performance Monitor to see how much data is being cached, and how many of your disk reads are being satisfied by the SSD cache.
The whole room to control 4 lines of steel was about 10' by 15' and was air conditioned. Today I work on stacking machines run by PLC's that could run that entire system.
It's been an amazing increase in technology over the past thirty years. Even PLC's now are miniaturized.
Very interesting.
I think the point of a smaller diameter platter and a more powerful motor is to spin the platter from zero up to max RPM instantly. Smaller diameters have less rotational inertia. I believe this affects seek time.
Did you ever do anything with an Altair? I’ve heard their last version was sometimes equipped with a hard drive or two as add-ons in addition to a pair of 8” floppy drives.
Rotating mass storage devices don't spin down, unless they are powered off. Some OS'es do so, if the power settings are set appropriately. Spinning up to RPM "instantly" is a massive amount of torque, even for the smallest disk, and it's not something you want to do repeatedly.
Rotational latency is determined by the speed of the disk, once it has stabilized. 4.2 milliseconds is the time it takes for a disk to rotate 180 degrees at 7200 RPM. That's where the "average" comes from: the length of time that you have to wait for a disk to rotate into position is -- on average -- 1/2 the time it takes to make a full revolution.
Did you ever do anything with an Altair? I’ve heard their last version was sometimes equipped with a hard drive or two as add-ons in addition to a pair of 8” floppy drives.
No, the stuff I worked on would fill a room, and heat several houses.
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