The Deskstar 7K1000 represents a milestone for Hitachi and for the hard drive industry as a whole, as it is the first drive to offer a 1 terabyte capacity. Honestly, I expected that it would be Seagate who would deliver the first 1TB hard drive since they were the first to reach the 500GB mark. However, Hitachi has not simply grabbed five 200GB platters and stuck them together to create a 1TB hard drive. Rather, there is much more to the Deskstar 7K1000, such as its Serial ATA II interface and the massive 32MB memory buffer. This is also the first desktop Hitachi drive to feature PMR technology (Perpendicular Magnetic Recording).
Perpendicular recording is said to deliver up to 10x the storage density of longitudinal recording, on the same recording media. There was some interest in using the system in floppy disks in the 1980s, but the technology was never reliable. Today, there is renewed interest in using it for hard drives, which are rapidly reaching their fundamental limits.
Current hard disk technology with longitudinal recording has an estimated limit of 100 to 200GB per square inch due to the superparamagnetic effect, though this estimate is constantly changing. Perpendicular recording is predicted to allow information densities of up to around 1TB/sq. inch.
Depending on how you see it, this 1TB Hitachi is realistically a 935.5 GB hard drive. Operating systems such as Windows use the binary approach to measure capacity. Hard drive manufacturers measure capacity using a decimal system instead, which means a single kilobyte equals 1000 bytes (the binary approach measures one kilobyte to equal 1024 bytes). Hard drive manufacturers have been using the decimal system as a form of advertising because it allows them to claim larger capacities. The issue of whether or not this is ethical can be argued, but these days it has just been accepted the way things are.
Windows shows the capacity of the Seagate Barracuda 7200.10 500GB hard drive to be just 457.2 GBs, which means two of these drives would actually offer slightly less capacity than a single Hitachi 1TB drive. However, two Seagate 500GB hard drives cost just $300, making them considerably cheaper than a single 1TB drive, and given that two drives should be faster than one, which configuration is really the way to go?
With this mindset we can start to play the different possible scenarios, for example, the obvious advantage of having a larger single drive is that there is less room required inside the computer's case, and only one SATA port needs to be used. There is also less heat produced and less power required. Another important consideration is that one hard drive is much quieter than having two or more. For Small Form Factor (SFF) and Home Theatre Personal Computers (HTPC) where space is tight, a large single hard drive can be invaluable.
Then again, two main negatives for owning a large single drive is that if it dies, all the data will go with it down the drain, and of course as we have covered, you do pay a price premium for having one large hard drive.