by Andrey Kuznetcov
02/22/2006 | 09:27 PM
In the beginning of XXI century the HDD manufacturers were under the influence of true euphoria. The transition to GMR-heads promised long-term prospects for further data density increase. All they needed to do was to continue reducing the size of the heads and the bit size in the platters magnetic layer, and they would be set for a long time.
They could report the launch of the new HDD family every 8-9 months, and the maximum storage capacity if the new drives would be 1.5 and maybe even two times higher than what the previous HDD family boasted.
However, this forecast never came true, just as any other long-term forecast. The problem was connected with continuous reduction of the magnetic bit size. The smaller got the bit, the higher was the probability that its magnetic polarity may change spontaneously due to the influence imposed by the magnetic power from the neighboring bits. Since with the current data density one domain contains just a few dozens of bits, then the oscillation of just one single bit may result into an avalanche-like phenomenon. Of course, in this case we should really worry about the data security.
What could be done to eliminate this threat? We cannot cover the plates with higher coercivity material, because in this case we will need to increase the GMR-heads size (because we will need a stronger magnetic field). And this is absolutely impossible, because the adapt density is directly dependent on the magnetic head size.
Is there any way to overcome this super-paramagnetic barrier? Yes, there is!
There appeared some hope when specialists who were threatened to lose their research and development grants remembered about the perpendicular recording technology, that has actually been know for years already. Not all the simple things are ingenious, but all the great things are truly simple, this is the fact.
The main idea behind the perpendicular recording technology is to aim the magnetic domains not along the heads trajectory but perpendicular to it.
This is what the traditional read-and-write head looks like in case of longitudinal recording:
We can see the reading part of the head – the GMR-element on the left. And on the right there is a horse-shoe shaped writing head. The magnetic field generated by the head is closed between the poles through a special shield directing the domains underneath it this or that way depending on the polarity of the current send to the head. As you can see from the picture above, the domains are directed in the longitudinal plane.
The read/write head for the perpendicular recoding technique looks like this:
Here you should pay attention to two key things. Firstly, the read head hasn’t been changed at all. Secondly, the write had seems to have got thicker on one end.
One pole of the new write head is considerably thicker than the other one. This, together with the special magnetic layer inside the platter, changes the magnetization direction. Now it penetrates the platter from the thin pole of the head goes into the magnetic layer and closes on the thick pole afterwards. The misbalanced density of the magnetic field resulting from different pole geometry allows recoding the data under the thin pole and “keeping them” under the thick pole.
Of course, to ensure that this method does work correctly, they had not just to change the shape of the read/write head but also to modify the platter. They needed to add this magnetic layer and… get rid of aluminum!
This is what the platter for perpendicular recording looks like if you cross-cut it. Beneath the protective overcoat there is the magnetic layer we are talking about. Under this layer there are two soft magnetic under-layers separated by the familiar AFC (AntiFerromagnetical Coupling). Even lower we see an adhesion layer and something else with a mysterious name “Substrate”. I believe here some of you will be astonished: this is a layer of glass!
Everything returns to its natural roots, and we see glass coming back to the hard disk drive industry. We only hope that the new generation adhesion material will boast better adhesive features to connect glass and metal layers.
But let’s return to the Soft Under-Layer. Note that you see a mirror reflection of the head in the magnetic under-layer in the picture with the perpendicular head. It is true, this layer turns into the second head “flying” beneath the magnetic layer.
The funny thing is that if you rotate both heads from the perpendicular recording illustration by 90 degrees to the right, we will see a head from the first picture! Nice perpendicular, eh?
It is always a pleasure to succeed in something. Seagate cannot be considered a discoverer of the perpendicular recording technology that allows increasing the storage capacity of the hard disk drives and improving their performance, and Seagate was not the first one to put it to practical use. Despite this fact, Seagate can still be considered a pioneer in this field to some extent, because they were the first ones to introduce this promising innovation in 2.5-inch HDDs. We are talking about Momentus 5400.3 hard disk drive family here. And this event is of truly remarkable importance. The thing is that there will be other HDDs with perpendicular recording technology from other storage manufacturers, which will boast much more attractive characteristics than the traditional models. And this will be the case not only for 2.5” devices, but we will also see 3.5” HDDs, which you might be more interested in, I suppose.
Since the HDD storage capacity remains one of the most important criteria for the computer users at this time, the HDD makers started introducing the perpendicular recording technology in the most compact devices first, because the storage capacity of this type of devices is more critical (for the users) and the maximum profit from a single HDD sale in this field is generally higher (for the companies).
We managed to get our hands on the Seagate Momentus 5400.3 HDD with the biggest storage capacity of 160GB. And of course, we couldn’t help comparing this drive with the solutions from other companies boasting at least 100GB of storage space and featuring the same spindle rotation speed. We have tested some if them before, so you can check for example this article for details. You can see the technical specifications of all the HDDs that participated in our test session here .
The family of hard disk drives designed with principally new technology includes 6 models with the storage capacities of 40, 60, 80, 100, 120 and 160GB. As we see from this list, the available product range allows the users to make the best choice for their needs. The HDDs feature 5,400rpm spindle rotation speed and 8MB buffer. The average seek time equals 12.5ms, and the latency is 5.6ms. All HDDs support Ultra ATA/100 interface. Among the distinguishing features of these drives the manufacturer mentions the special highly robust design that ensures that the HDD will stand higher shock: up to 350Gs operational shock and up to 900Gs non-operational shock. Seagate stressed that despite the 5,400rpm spindle rotation speed the actual power consumption of the 5400.3 HDD models equals to that of the solutions with 4,200rpm spindle rotation speed. The performance of the new drives is also claimed to be 50% higher.
As for the price of this new drive it is not selling widely yet, but it is anticipated to appear in stores soon for about $400 in the beginning.
For our today’s test session we used the following software:
We assembled the following testbed:
The tests were performed with the “default” OS drivers. The drives were formatted for FAT32 and NTFS file systems as a single partition with the cluster of default size. In some cases, which will be specifically mentioned later in this article, we tested 32GB logical partitions, also formatted for FAT32 and NTFS systems with the default cluster.
The low-level Intel IOMeter benchmark was used to test the linear read and write speed of the hard drives. During the test session there was a stream of read/write requests sent to the drives with the queue depth=4. The data block size changed every minute. As a result we can see the dependence of the linear read/write speed on the data block size.
At first let’s take a look at the linear read speed. On the first diagram we can clearly see that the performance difference between the Seagate Momentus 5400.3 (ST9160821A) and the rest of the test participants. The new HDD is evidently faster than the opponents when we come to the data block size of 8KB and up.
The second diagram shows the linear write speed. We notice right away that the picture is very similar to what we have just seen in the previous case. Once again Seagate Momentus 5400.3 (ST9160821A) outperforms all the other hard drives starting with 8KB data blocks.
This way, the effect from the new technology on the read and write speeds is indisputable.
The moment we look at the linear reading graph we see that the new HDD shows excellent results thanks to its higher data density. Note that the line on the diagram doesn’t have any clear-cut steps with long horizontal segments.
The thing is that Seagate used the adaptive formatting technology in its new drive. This technology implies that for each surface-head pair the best algorithm for the most optimal zonal density distribution is selected, which offers the best combination of performance and reliability.
If the parameters of the head and platter are high enough, more sectors can be placed on a single track and the longitudinal density increases. If the head or the platter leaves more to be desired, there is still nothing to worry about: there will be more tracks arranged on this surface.
By the way, this technology gives way to the notion of “N-gigabyte” platters, i.e. the fact that the capacity of each selected platter doesn’t necessarily have to equal one half or one third of the HDD capacity. Because it is quite possible that there not very good heads o both sides of the platter. However, this is nothing you should worry about because you can still reach the desired total drive capacity at the expense of other platter(s). Or in the worst case you might have to make the HDD one grade smaller.
The major advantage of this technology is the fact that you do not have to check the heads parameters similarity before the heads block assembly and this way we can completely eliminate the defective drives from the production increasing the yields to 100%.
So, how could we find out what’s inside the new HDD? How many sectors per track does the new drive have? And what is the difference between the data density on different HDD surfaces?
Since these new HDDs use adaptive formatting, each of them is actually unique. Our drive has the following zone map:
The diagram above shows the real density zone map for each of the read/write heads. We can see very well that this map is unique for all four heads. It is also remarkable that each surface has different number of tracks.
By the way, this is one of the reasons for somewhat unstable results of random access time measurements. Since most tests use not too many requests for random access time measurements (usually 256-2500 requests), the requests get distributed between the platters unevenly.
As for the data recording density, we managed to reach the SPT (SectorPerTrack) of 1120 sectors for two heads. If it hadn’t been for the low spindle rotation speed, Momentus 5400.3 could outperform even Barracuda 7200.7 in the linear read speed.
Let’s see how the perpendicular recording technology affected the overall HDD performance in Disk WinMark. At first we will check the FAT32 file system:
The results on the diagram are somewhat surprising. The results of the most interesting test in this case, High-End Disk WinMark, put Seagate Momentus 5400.3 (ST9160821A) not in the best position, as it has been left tangibly behind by Fujitsu MHV2100AH. The same happened in Business Disk WinMark. Unfortunately, our hero won only the second prize.
Now let’s take a look at the HDD formatted for NTFS file system:
According to the benchmark results shown on the diagram, the situation with our Seagate Momentus 5400.3 (ST9160821A) hasn’t got any better. Moreover, the Momentus 5400.3 fellow was only the fourth to finish this test in High-End Disk WinMark.
The linear read speed diagram showing the results in the beginning and in the end of the HDD reveals the triumph of the perpendicular recording technology: Seagate Momentus 5400.3 (ST9160821A) is an undefeated leader.
The last diagram of this section is devoted to the access time. Seagate Momentus 5400.3 (ST9160821A) performed pretty well here, although it didn’t manage to take the lead.
Now let’s take a look how Seagate Momentus 5400.3 (ST9160821A) is going to perform in FC-test. This benchmark produces the most realistic performance results, because the algorithms used in this suite create real-life situations.
The credibility of the results is based on the working principles of this program. The main idea of FC-Test is to measure the time the hard disk drives need to create (write), read and copy file sets, which differ from one another by the type, size and number of files. Then we calculate the practical performance of the drives basing on the time measurements.
As you remember from our previous HDD reviews, Windows and Programs patterns include a large number of smaller files, and the remaining three patterns – ISO, MP3 and Install – work with a limited number of larger files. For copy operations each drive is formatted into two 32GB equal logical partitions. The patterns are copied either within the same partition or from one partition to another. Although the tables contain complete performance reports, we decided to use the results of only three patterns for the illustrative diagrams. The hard disk drives were grouped according to the manufacturer, and the closest drive to our new Seagate Momentus 5400.3 (ST9160821A) is the one with 120GB storage capacity.
Let’s discuss the results in greater detail. We will start with FAT32 file system. Note that we do not have the results for Hitachi HDD, because it failed this test completely.
On the first diagram we seer the file writing (creating) speed. Seagate Momentus 5400.3 (ST9160821A) appeared the fastest of all having demonstrated almost the same speed as its 120GB relative. The gap is especially big when we get to work with sets of larger files.
The next diagram shows the read speed of the hard drives. Seagate Momentus 5400.3 (ST9160821A) outperforms its opponents here, too: its advantage is beyond all doubts.
File copying within the same partition is done fastest of all by our new Seagate Momentus 5400.3 when it comes to large files. However, when we are working with smaller files, the newcomer starts losing its positions to the major competitor from Fujitsu and the predecessor – Seagate Momentus 5400.2 (ST9120821A).
When the files are copied from one partition to another, Seagate Momentus 5400.3 (ST9160821A) doesn’t differ much from the Momentus 5400.2 (ST9120821A). they both performed almost equally fast, but the latter appeared just a tiny bit faster.
Now we have to pay some attention to the results in NTFS file system:
During file writing (creation) Seagate Momentus 5400.3 (ST9160821A) manages to get fast enough to follow close behind the leader, its predecessor – Seagate Momentus 5400.2 (ST9120821A). Our newcomer fell just a little bit behind the leader, and even dashed ahead in one of the patterns.
The read speed of Seagate Momentus 5400.3 (ST9160821A) was high enough to bring it the absolute victory. In three patterns out of five it was faster than its two major opponents: Fujitsu MHV2100AH and Seagate ST9120821A.
The diagram with the file copy results obtained within the same partition gives us to understand that Seagate Momentus 5400.3 (ST9160821A) runs practically as fast as Fujitsu MHV2100AH and Seagate Momentus 5400.2 (ST9120821A). So, we see evident parity here.
The last diagram gives us an idea about how fast the files can be copied between partitions. Once again we see that there is no absolute performance leader here, but if we take into account the results obtained in all five patterns then the laurels will be given to Seagate ST9120821A. Our today’s main hero wins the prestigious second prize because it is generally faster than one of its major rivals – the Fujitsu drive.
We once again resorted to PCMark04 to get a better look on the performance of our today’s hero.With this benchmarking suite we will test the performance of our hard disk drives in five different modes. You can read more about PCMark04 benchmark and its advantages for HDD testing in our article called “PCMark04: Benchmark for Hard Disk Drives? ”.
Windows XP Startup test contains a sequence of requests sent to the HDD on system start-up. Application Loading test shows disk activity when the system opens and closes six popular applications. File Copying test shows the HDD activity when copying a set of files. Hard Disk Drive Usage reports the disk activity during the work with some widely spread applications.
Having run all the tests for a given HDD, PCMark04 generates a certain performance index calculated according to the following formula:
HDD Score = (XP Startup Trace x 120) + (Application Load trace x 180) + (File Copy Trace x 28) + (General Usage x 265)
In our case we ran each test 10 times, calculated the average values and summed them all up in the table and diagrams below.
The first diagram shows that the new Seagate Momentus 5400.3 (ST9160821A) is the third in Windows XP Startup test having let Seagate Momentus 5400.2 (ST9120821A) and Toshiba MK1032GSX ahead.
The situation is somewhat worse when we get to the Application Loading parameter. Unfortunately, our new drive was the very last one here having fallen far behind the rivals.
The results of File Copying are finally a pleasing sight. In this case Seagate Momentus 5400.3 (ST9160821A) is an indisputable winner.
Another parameter we are looking at here is HDD Usage. And again the results are quite disappointing. Although this time Seagate Momentus 5400.3 (ST9160821A) is not the last one: the last but one :)
The summary diagram indicates that Seagate Momentus 5400.3 (ST9160821A) didn’t really prove a powerful and strong solution in this test. Hopefully, the mass production units will be better…
So, what are the main attractive features of the new Seagate Momentus 5400.3 (ST9160821A) hard disk drive with perpendicular recording technology? Of course, the primary advantage is its high storage capacity. Thanks to 160GB of storage space it has simply no competitors in this field. If the storage capacity is a crucial parameter for you, then Seagate Momentus 5400.3 (ST9160821A) is definitely the way to go. Second important feature of this drive is its performance. As our tests showed, even though Seagate Momentus 5400.3 (ST9160821A) didn’t win in all the benchmarks and patterns it proved pretty fast in most real-life tests and outpaced the competitors in the majority of them.
So, Seagate Momentus 5400.3 (ST9160821A) presents a perfect combination of big storage capacity and quite high performance, which turns it into an optimal choice for most needs. The high price of the new HDDs will inevitably go down now that the drives started selling, because the competitors will not sit idle and there will be more and more HDDs with perpendicular recording technology in the market. By the way, as we have seen in the linear reading and writing tests, this new technology managed to significantly increase the linear speeds having created a good basis for further performance improvement.
Now we are looking forward to perpendicular recording technology implementation in 3.5-inch HDDs!