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Perpendicular Hard Drive Recording Technology

How can a 3.5-inch standard hard disk drive (HDD) possibly hold a terabyte of information? As manufacturers reached the limits of hard drive capacity, consumer demand for even higher capacity drives did not diminish. A relatively new recording technology called perpendicular recording, is being deployed to further increase hard drive storage capacities.

Recommended Reading:
For those unfamiliar with how hard drives work, we recommend you first read "Did You Know... What's Inside a Hard Drive?"

To understand how perpendicular recording has changed hard disk storage and increased storage capacities, you first need to understand conventional, longitudinal recording.

Longitudinal Recording
As indicated by the name, longitudinal recording is a method of recording data to a hard disk drive (HDD) in such a way that the data bits are aligned horizontally in relation to the drive's spinning platter, which is parallel to the surface of the disk. Essentially, you are recording on a magnetic material, where bits (a collection of magnetized particles) are laid out end-to-end. Longitudinal recording is the actual method of how the bits are recorded on disk platters. The direction of this magnetic charge is horizontal to the media, meaning the north and south poles of the magnetized particles are lined parallel to the surface of the disk.

Longitudinal recording has been the standard method of recording for more than 50 years — the first commercial hard drive was introduced in 1956. Over the years we have seen many technological changes to longitudinal recording, which have resulted in higher-capacity drives. We've moved from 5.25 inch drives to 2.5 inch drives, the number of platters and heads have been reduced all the while increasing areal density (which is the amount of data per square inch of media).  With all of these changes however, the need to physically change the way data was written to the drive was also being considered to reach higher storage capacities.

Key Terms To Understanding Perpendicular Hard Drive Technology:

Short for hard disk drive.

hard disk drive
The mechanism that reads and writes data on a hard disk.

longitudinal recording Longitudinal recording aligns data bits horizontally in relation to the drive's spinning platter, parallel to the surface of the disk.

perpendicular recording
Perpendicular recording aligns data bits vertically . perpendicular to the disk.

The fluctuation of magnetization due to thermal agitation.

areal density
Also called bit density. The amount of data that can be packed onto a storage medium.

A round magnetic plate that constitutes part of a hard disk.

Storage capacity with longitudinal recording was largely increased by decreasing the size of the magnetic grains that make-up data bits. As the magnetic grains became smaller, more data could then be stored on the disk. Unfortunately, magnetic grains have their limits. By continuing to shrink them, the point where data integrity would be compromised was on the horizon. This effect is called the superparamagnetic effect.

Image Source: Hitachi Global Storage Technologies - Perpendicular Recording

The Superparamagnetic Effect
In magnetic disk drive storage technology, the superparamagnetic effect refers to the fluctuation of magnetization due to thermal agitation. When the areal density (the number of bits that can be stored on a square inch of disk media) of a disk medium reaches 150 gigabits per square inch, the magnetic energy holding the bits in place on the medium becomes equal to the ambient thermal energy within the disk drive itself. When this happens, the bits are no longer held in a reliable state and can "flip," and scramble the data that was previously recorded.

Because of superparamagnetism, hard drive technologies were expected to stop growing once they reached densities of 150 gigabits per square inch. Of course, when you see a hard drive manufacturer announce a 400GB hard drive you may wonder what happened to the superparamagnetic effect? Actually, this type of drive would contain three platters able to store up to a maximum of 133GB each resulting in a 400GB HDD, it is not 400GB contained on a single platter.

Perpendicular Recording
Realizing the limits of packing smaller magnetic grains was heading towards occurrences of superparamagnetism, manufacturers still needed a way to pack more data onto each drive. Perpendicular recording differs from longitudinal recording in that data bits are aligned vertically (not horizontally) — or perpendicular to the disk, which allows for additional room on a disk to pack more data, thus, enabling higher recording densities. It is widely believed that with perpendicular recording, the superparamagnetism barrier can be pushed further back allowing for continued growth in the areal density of the media for some time.

Image Source: Hitachi Global Storage Technologies - Perpendicular Recording

Hitachi believes this recording technology, in time, can result in a 3.5-inch disk drive capable of storing an entire terabyte of data. Not only will perpendicular recording have an effect on desktop storage, but on consumer devices as well, which is a major driving force in storage sales. Smaller drives (1.8 inch), like those used in the popular Apple iPod will also grow in capacity .  in due time we will see the iPod and similar devices offer 80GB of storage and higher. Alternatively, it could be used to produce much thinner and slimmer high capacity hard drives for consumer devices. Where you can store 3,000 on some of the higher-end MP3 players today; image being able to store 30,000 songs on one.

Perpendicular recording technology however will not start and stop with changing the way data bits are aligned. Much like the growth in capacity with longitudinal recording, technological advancements in platters; read/write heads, and physical disk media surfaces to name a couple, will contribute to advancements in the capacity growth of perpendicular hard disk drives.

Perpendicular recording technology also is not the answer to removing superparamagnetism. It has not stopped the search for the ever elusive answer to being able to further shrink the actual size of the magnetic grains that make up data bits.  Perpendicular recording only moves the superparamagnetism barrier back a bit, it doesn't eliminate it. For now Perpendicular recording technology allows for many new developments and advancements in storage capacity over the coming years, but it too will feel eventually feel the pull of the  superparamagnetic effect; unless the physical size of a bit can be further reduced, then again that barrier will be pushed back to meet the ever-growing storage needs of consumers.

Did You Know...
According to iSuppli, the global hard disk drive (HDD) industry set an all-time record for growth in 2005, with shipments rising to 71 million units for the year.

Vangie 'Aurora' Beal
Last updated: April 21, 2006

Related Links

Hitachi "Get Perpendicular"
A fun Macromedia Flash animation by Hitachi Global Storage Technologies called "Get Perpendicular". Through music and animatuion this flash describes Perpendicular technology. To view the animation you will need the Macromedia Flash plug in.

Perpendicular Recording: A Boon for Consumer Electronics
While the hard drive industry has been using longitudinal recording successfully for five decades, it is now within two product generations of reaching its practical limit. For about the past decade, scientists and engineers have pondered the potential effects of a natural phenomenon called superparamagnetism and postulated when its presence might interfere with the progress of the hard disk drive (HDD) industry.

Did You Know... What's Inside a Hard Drive?
All hard drives share a basic structure and are composed of the same physical features. However, not all hard drives perform the same way as the quality of the parts of the hard drive will affect its performance.

Seagate Technology Squeezes 160GB of capacity onto a 2.5-inch Disk
How did Seagate Technology squeeze a new-record 160GB of capacity onto a 2.5-inch notebook PC hard disk? The Momentus 5400.3 is the company's first laptop drive that uses perpendicular recording -- data bits that stand up instead of lying down on the platter -- to deliver areal density of 132 gigabits per square inch.

Toshiba Storage Device Division
Tosbiba CE and HDD products.

CNN Money - Seven New Technologies That Change Every Thing
With perpendicular storage, each bit occupies less space on the surface of the disc, so more data can be stuffed into a smaller area. In addition, because the data is more densely packed, the read-write heads don't shuttle around as much, so PMR drives draw less power from overworked batteries.

Wired News: Hard Drives get Vertical Boost
Seagate's new drive, the Momentus 5400.3, was being shipped as of Monday, the Scotts Valley, California-based company said. The shift to perpendicular recording allows it to bump up the maximum capacity of its notebook drive to 160 GB from 120 GB.

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