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Perpendicular Recording

by Parm Mann on 20 October 2008, 00:00

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This HEXUS.help guide explains what perpendicular hard disk recording is, why it matters and what disks currently support it.

The Technology

With hard disk capacities reaching some tough physical limits with longitudinal recording, as manufacturers struggle to improve aereal density of HDDs as they approach 1TB in capacity, the disk vendors have had to come up with better ways to pack data onto a disk's platters.

We mentioned longitudinal recording for a reason, so let's explain that first. Hard disks work by a read/write head passing over a spinning platter, where the head sets the orientation of a magnetic field which represents a single bit of data on the disk. The platters pack these individual magnetic regions close together in order to achieve high data density.

Longitudinal recording lays the fields out flat. Think of a woman lying on her back, in terms of physical orientation. Now imagine how many women you could fit into a given area, should they all be lying down like that.

Now think of how many women you could get into the same space if they were all standing up. Makes sense, therefore, that hard disk vendors would start to think about orienting the magnetic regions on a disk platter in much the same fashion. Performance and aereal density can rise usefully, and costs can come down for drives of the same size, due to less platters being needed for the same space.

How it works

The concept is a simple one. Use a 'strong' magnetic material with a higher coercivity (field intensity) than used on previous disks, and a new read/write head that's able to work with the material layer in such a way that manipulating single bits on the platter is a possibility.

The higher intensity makes it possible to keep bits stable when perpendicular to the surface, and crucially stable at operating temperature. That's pretty much it.

Drives using the new technology

Toshiba were the first to market with a 1.8" portable disk, with Seagate not far behind with their 2.5" Momentus 5400.3 range (160GB version here). For desktop PCs, Seagate's Barracuda 7200.10 range on both PATA and SATA interfaces uses the technology, and for server and high-end workstation applications you can look for Seagate's Cheetah 15K.5 disks, up to 300GB in size and using SCSI.

What it means in the future

Perpendicular recording for hard disks is the next step in creating high-density disks to match current form factors. It's simply a means to cram more data into the same space. Think in the future of iPod Mini-sized devices with 60GB or more, desktop HDDs with well over 1TB and notebook HDDs exceeding 500GB.

More data in the same space is what it enables, mainly. Almost all magnetic HDDs in the long-term future will make use of the technology, so you'll get it by default.

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