Given the IDEMA’s statement that all drive makers will transition to Advanced Format as of January, 2011, this article has been substantially updated.
Another limit is being pushed in computers: The 32-bit LBA addressing mode. Hard disk drives have simply become too big for the 2.1 TB allowed by 32-bit LBA and 512 K sectors. Western Digital was first to answer this challenge with “Advanced Format“, and Seagate took an alternate 48-bit LBA route while also supporting AF. Now Hitachi GST introduced an Advanced Format drive of their own. Will the industry ever adopt 48-bit LBA?
Two Options Past 2.1 TB
As explained in detail in my piece, Taming Monster Disk Drives: 3 TB and Beyond!, the current hard disk addressing scheme tops out around 2.1 TB. There are two simple factors in this equation:
- There are 4,294,967,296 addressable blocks in a 32-bit “namespace”, and this is all most PCs can handle
- Each block is 512 bytes in size, and has been since dinosaurs sold the computers
If we multiply 4,294,967,296 times 512, we get 2,147,483,648 KB of capacity. In wacky base-10 storage industry speak, this is 2.15 TB of capacity. No hard disk drive can be larger than this while obeying these limits.
The solution to the problem is simple: Increase one value or the other and the issue vanishes. Although older computers can’t handle a change to either, it’s equally simple to engineer hardware and software that can.
The hard disk drive manufacturers have two roads forward, and they are not mutually-exclusive:
- Western Digital was first out with an “Advanced Format” drive late in 2009. This addresses the (archaic) block size limit, increasing it from 512 bytes to 4 kilobytes. With each address now eight times larger, we need one-eighth as many addresses for a given drive size. Advanced Format drives can grow to 16 TB without hitting the 32-bit LBA size limit.
- Seagate attacked the other variable, increasing the address space to the full 48 bits specified in the LBA standard. This gives an amazing 128 petabytes of capacity even with tiny 512 byte blocks.
Both of these solutions have issues with older systems, but many current machines can handle either with ease. Apple Macintosh machines are set, since they use modern EFI firmware and have had capable driver software since OS X 10.4 “Tiger”. PCs running recent versions of Windows can generally use larger disks as long as long as they don’t try to boot from them. External USB or FireWire drives ought to be fine with every computer, too.
Hitachi GST Joins Western Digital With Advanced Format
The 4K “Advanced Format” solution is gaining traction, with both Western Digital and Hitachi GST currently selling drives supporting it. Seagate introduced 48-bit addressing and has also begun to support Advanced Format, quietly introducing the technology in their Momentus line. Toshiba and Samsung are expected to adopt Advanced Format soon as well.
Interestingly, Hitachi GST introduced Advanced Format on a line of 2.5-inch drives that top out at just 750 GB. It is curious that they chose to introduce it in a product line that will not likely breach the 2 TB limit in its lifetime. It is likely that this is a sign of the company’s commitment, however, and that future 3.5-inch products will share the same Advanced Format controller chipsets used here. See the excellent Hitachi Advanced Format brief for more information on the technology.
I see the innovations of 48-bit LBA and Advanced Format as a welcome sign of change in the hard disk drive industry. Inevitably, both variables must be addressed: 512 bytes is simply too small for modern applications, and the 32-bit LBA limit will inevitably become a constraint regardless. The industry must push both forward sooner or later, and I am glad to see it happening even if only in pieces.
The PC makers’ stubborn support of BIOS and MBR is much more of a concern. Switching to a modern system firmware like EFI would only cost a few pennies, and modern operating systems are ready for the change. Indeed, a few PCs come with EFI already, and Apple adopted it wholesale years ago. Similarly, GPT is ready to take over for MBR if only the PC software makers would stand and support the change.
MBR and BIOS are the real enemies here, whether we are discussing hard disk drive formats or filesystem limitations. Backwards compatibility is nice, but the Wintel PC world will be forced to make the change eventually. Since external hard disk drives work equally well regardless of partition scheme and most PC users will never upgrade their hardware, maintaining BIOS and MBR in PCs is really a question of penny-pinching anyway. It’s time for Microsoft to push PC vendors to make the change.
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