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The concept of perpendicular recording (PR) has been getting a lot of press lately, and has finally been engineered into something we can actually get our hands on. For the longest time, hard drive capacities seemed locked at 250 GB, a temporary wall only recently broken down. Hitachi was the first to offer a larger capacity 500 GB drive, but the process used to achieve that size involved the traditional method of longitudinal recording as well as a large number of rotating discs (so-called platters). Now we've got the first of the perpendicular drives on our testbed with others sure to follow soon.
Before we get to the results, let's briefly go over how perpendicular recording technology works. Traditional hard drives store the bits in a linear (or longitudinal) fashion upon the surface of the drive platter. Perpendicular recording changes the ballpark by re-orienting the manner in which information is written to the disk. Particles are now magnetized along a vertical, circular path instead of a linear one. By recording bits vertically (perpendicular to the platter surface), drive makers can fit more information onto available drive space, creating potentially much higher data density (called areal density).
The platters for perpendicular drives are thicker to allow for the new data orientation, and a soft underlayer has been added beneath the recording surface. Not only is the space that is occupied by the data compressed, but the "transition region" that marks the beginning of the next chunk of information is also effectively reduced. Despite the change in technology, the Barracuda uses the same 3.5" form factor as any other desktop drive.
When recorded in a longitudinal fashion and compacted into a very small space bits can "flip" magnetic orientation, which causes data corruption. This tendency to magnetically "flip" particles with too small a charge is known as the superparamagnetic effect. With longitudinal recording, a high areal density is difficult to achieve: should the bit area become too small, it loses the amount of charge needed to keep its magnetic charge intact. Perpendicular recording allows for more condensed storage of information since the magnetism of the data is not compromised as easily as in small areas along the vertical recording line. Since there are only so many bits that can be packed onto a finite space, linear hard disk recordings max out at 100 to 200 Gb/in². Perpendicular recording is expected to increase the amount of available storage space to up to 5-10 times that or around 1 Tb/in².
Hitachi has a fantastic (well, and somewhat cheesy) "School House Rock" style flash animation on the technology, which can be found here.
There have been a few other changes in terms of hard drive technology. 2003 brought the dawn of Serial ATA, which had the potential to blow the data transfer capability formerly allowed by ATA/IDE out of the water. First generation Serial ATA allows for maximum transfer rates of 150 MB/s running at a clock speed of 1.5 GHz. The Intel 945/955 and Nvidia nForce4 chipsets doubled this transfer rate to 300 MB/s by increasing the transfer speed of the serial connection to 3 GHz. All drives in this comparison run SATA/300, but as discussed in previous Tom's Hardware articles, real world data rates can be disappointing when compared with the hypothetical. The main reason is that data rates to and from the magnetic platters max out at around 90 MB/s today. The Western Digital WD1500AD Raptor-X works the Serial ATA 150 interface to its advantage and consistently reports better numbers than all other desktop drives - including many RAID setups.
One important factor in what we call the "speed pipeline" of a system is the frequent need to wait for data delivery by the hard drives. RAM/CPU speed takes a back seat to hard disk speed when it comes to actually getting at data. This can lead to those debilitating system hiccups we're all too familiar with. A user wants that perfect blend between size, speed and price for his or her system hard drive. So without further ado let's get to the heavyweight contenders in the size arena.