The Tech Report takes Hitachi’s new 1 Terabyte hard drive for a spin.

We’ve been able to have over 1 terabyte of hard drive space in our personal computers for awhile now by doubling up on 500GB or higher hard drives, but this is still a milestone as it’s the first consumer level hard drive to lay claim to being a terabyte in a single drive. The folks over at The Tech Report got their hands on one to test it out, but first they discussed the age-old problem of when a terabyte isn’t really a terabyte:

By now I’ve no doubt been heckled by someone insisting that the 7K1000 doesn’t actually offer a full terabyte of storage capacity. This person probably sounds like the comic book guy from The Simpsons, but don’t dismiss him. He has a point, sort of.

According to the International System of Units (SI), a terabyte consists of 1,000,000,000,000 bytes—10004, or 1012.  Windows confirms that the 7K1000 delivers 1,000,202,240,000 bytes, which is more than it needs, so what’s the comic book guy on about?

Look a little closer, and you’ll see that while the 7K1000 does indeed offer over a trillion bytes, that capacity only translates to 931 gigabytes.  For an explanation of why, we have to delve into the always exciting world of numerical systems.  SI units are built on the same base 10 decimal system we’ve been using since grade school.  Computers, however, use a binary base 2 system.  So, while a kilobyte in decimal is 1,000 bytes, a kilobyte in binary translates to 1,024 bytes.  A binary terabyte, then, is not 1,0004, but 1,0244, or 240.

Multiplying that out, a binary terabyte yields 1,099,511,627,776 bytes, which is why the 7K1000 falls short of a thousand gigabytes. The drive would actually need 1,024 gigabytes to achieve terabyte status in the binary world. This translation problem isn’t unique to the 7K1000, either. Virtually all hard drives advertise their capacities in SI units, so their actual capacities fall short of binary expectations.

The discrepancy between the stated size on the box and what you actually see once it’s installed in your PC has been the source of grumbling for years now, but really hasn’t come to a head. I suspect, however, that with the gap being what amounts to what was once a hard drive unto itself (69GB) that said grumbling may grow a little louder as capacities—and the associated gap—continue to increase.

But that’s being nitpicky. The real question is how well does the drive perform? According to the folks at TR it performs pretty well, but not so well as to justify its price compared to some of the smaller, smaller being a relative term here, and cheaper drives such as the Western Digital 750GB Caviar SE16. This is particularly important when you consider that you’re probably going to want two drives to set up a mirrored RAID array in case one of the drives fail because 931GB is a lot of data to lose to a hard drive failure.

Still, kudos to Hitachi for being the first on the market with a hard drive that us old timers once only dreamed of. I won’t be getting one anytime soon as I’m still finding I have plenty of room on the measly little 320GB hard drive in my current machine, but with the impending release of Windows Home Server it may not be that far off in the future that I’m looking for lots of storage space.