Sunday, April 10, 2011

Windows 7: 3TB Hard Drives (and Larger)

If you try to mount that 3TB (or Larger) hard drives (HDD) or solid-state drive (SSD) on a computer, you will soon notice that Windows can only address 2.19TB of storage. This is a limitation of the current standard method of storing data on a drive partition that utilizes 32-bit LBA (Logical Block Addressing).
For those who like technical information. LBAs are stored linearly, starting at LBA 0 up to the last address on the device. The amount of LBAs that can be accessed are a function of the type of partition applied to the drive when it was formated.

LBAs under most MBR (Master Boot Record) partitions use 32-bit address values, with the maximum value being 2^32 or 4,294,967,296. Each LBA on the drive corresponds to a 512-byte sector value (this also applies to 4K formated drives, they still appear as 512-byte sector drives to the OS). The largest available 32-bit MBR partitioned drive can be 4,294,967,296 * 512-bytes or 2,199,023,255,552 bytes (or 2.199TB).
To overcome the 2.19TB limition of the 32-bit LBAs, a new partition type was created called GPT (GUID Partition Table) supports 64-bit LBAs. Using 64-bit LBAs, the largest 512-byte sector drive that can be addressed is 9.4ZB (Zettabytes - or 2^70 bytes).

Depending on the age of the computer and the functionality contained in the version of the BIOS that is installed, it may are may not support booting from a partition that is larger then 2.19TB in size. Although, that doesn't mean that you can't create secondary partition that are larger then 2.19TB as long as the hardware (e.g. drive controller and software drivers) and version of OS support it.
  • Intel’s Extensible Firmware Interface (EFI) the successor to the PC's BIOS supports GPT boot partitions. 
  • All x64 versions of Windows (Windows XP, and higher), Mac OSx, and Linux should support GPT partitions.
If your current x64 OS and hardware doesn't support GPT partitions, you can buy a drive controller that supports the larger GPT drives as long as you have a computer that supports its system requirements.

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