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Ever since hard drives went mainstream in the late 1980s, computer owners have been able to count on one thing: their increasing capacity. As a result, what once used to be little more then a convenient method for reducing disk swapping has now become an integral part of daily life, with hard drives today storing not just our programs and our documents, but our very memories in the form of the photos and videos. The ever-increasing numbers of those have forced storage capacity to skyrocket to still more dizzying levels, to the point where most ordinary people now only really think of it when they’re in danger of filling it up. But there’s a reason that really large hard drive should be at the forefront of every computer owner’s mind: they’re about to become unusable.
Okay, perhaps that’s a bit hyperbolic but only a bit. The fact is, we’re not just approaching the threshold at which hard drives can’t get bigger: We’re already there. The advent of very large hard drives, we’re talking over 2.19 terabytes (TB) in capacity, in 2010 has highlighted a problem that’s been growing for well over a decade, and whose seeds were planted when the very first hard drives hit the market some 25 or 30 years ago. The good news is that there are some solutions to it; the bad news is, they’re little more than workarounds for an issue that needs more than makeshift bandages.
What Is the 2.19TB Barrier?
Back in the days when hard drives’ capacities were measured in megabytes at the outside (we’re talking the 1950s here, though it was still the case well into the 1980s, when floppy disks’ sizes were measured only in kilobytes), a block size of 512 bytes made sense as a way of maximizing available space. But during the boom years of the 1990s, when drives were rapidly getting bigger and performance started straining, the 512-byte block size became more restrictive. So the industry decided to up the standard block size to 4,096 bytes , or 4KB (sometimes referred to as “Advanced Format”); 4KB blocks have more efficient methods of error checking, which mean they can devote less space to it, resulting in drives of higher capacities and those that encounter fewer errors.
It was a good idea, but it didn’t gain mainstream adoption until after Windows XP made its big splash in 2001. That OS creates primary disk partitions at logical block address 63, just short of being perfectly divisible by eight, so it writes data across both sides of the physical boundary of the 4KB sector. In other words, the world’s most popular operating system for the better part of a decade didn’t support 4KB blocks, which put a huge crimp in the industry’s efforts to expand the initiative. Luckily, there was a way around this problem that could both benefit Windows XP users and ease the transition for everyone to the larger block sizes: Hard drives would report their blocks as only being 512 bytes in size, so any OS that didn’t understand the larger sizes could just “see” each 4KB blocks eight 512-byte blocks. Windows XP, then, would just need to “align” its sectors properly; that was hardly an insurmountable problem and, indeed, Western Digital has designed software to compensate.
Unfortunately, even 4KB sectors couldn’t guarantee drives of infinite capacity. Because of the limitations of the BIOS and 32-bit MBR partition in the earliest years of computing, hard drive capacities had a firm upper ceiling of 232 logical blocks. If each of those blocks was 512 bytes in size, that meant that MBR drives could store no more than 2,199,023,255,552 bytes, or 2.19TB.
More Problems and More Solutions
For computers to recognize drives any larger than 2.19TB, the MBR and the BIOS would have to be replaced. The successor to the MBR is the GUID Partition Table (GPT), which offers 64-bit block addressing , and thus (when 4KB blocks are utilized) a maximum storage size of 9.4 Zettabytes (or 9.4 trillion gigabytes). What’s supplanting BIOS, which can’t read GPT, is the Unified Extensible Firmware Interface (UEFI), which is built on CPU-independent architecture and drivers and offers more flexibility and features outside of the operating system. BECAUSE Windows XP has no support whatsoever for GPT and UEFI, no system running it can natively use any drive with a capacity over 2.19TB.Even if you have a supported OS (Windows Vista, Windows 7, and most flavors of Linux) that recognized GPT, you won’t be able t5o boot to a drive of that size unless you also have a motherboard running UEFI-something that, as of this writing in late 2010, very few do. All current Intel boards support UEFI, but almost no other major manufacturer has yet followed suit. So, under most circumstances, if you don’t have a UEFI motherboard (and you probably don’t), you’ll have to use your extra-large hard drive for storage only. (There are worse things.)
Finally, your system’s SATA controller must also be designed to recognize 4KB blocks. This isn’t necessarily a big deal: As we discovered when we reviewed Western Digital’s new 3TB Caviar Green hard drive, the company is including with all its above 2.19TB drives a PCI Express x1 Host Bus Adapter that lets Windows use a known driver to communicate with the drive.
What Does the Future Hold?
Right now, there aren’t a lot of compelling reasons for most home users to worry about drives larger than 2.19TB. Factor in the compatibility problems, and you’re investing more money and time in a product than you may necessarily want to. Right now, the less expensive, faster, easier-to-understand-and-configure storage is the better choice all the way around.
This isn’t to say this be the case forever-or even for very long. As of this writing, Asus has just introduced a software app called Disk Unlocker that will let users partition storage space above 2.19TB as a virtual drive. But it has a bunch of restrictions, not the least of which is that it only works with Asus motherboards. It’s an imperfect fix, but it shows what’s possible.
It also shows how far we still have to go. In many cases, the software irritations have already been soothed: 64-bit operating systems now make up a vast percentage of the market; and Windows XP is slowly fading away, and with it MBR. That leaves the current bottleneck as hardware: The only surefire way to deal with these problems once and for all is for motherboard manufacturers to universally implement UEFI and use SATA controllers that recognize 4KB blocks, two things that haven’t happened yet. Herd drive makers agreeing on 2011 as the first official year in which 4KB blocks the exception is a good first step, but it can’t be the last one. We have no doubt that WD and other hard drive companies will continue pushing the boundaries of storage capacity. But right now, too few users are properly equipped to follow where they’re leading.