Interface size limitations

Due to lack of foresight the first drive interface used 22-bit addressing mode which resulted in a maximum drive capacity of 2 GByte. Later the first formalized ATA specification used a 28-bit addressing mode, allowing for the addressing of 228 268 435 456 sectors (blocks) of 512 bytes each, resulting in a maximum capacity of 128 GiB (137 GB).

ATA-6 introduced 48-bit addressing, increasing the limit to 128 PiB (144 PB). As a consequence, any ATA drive of capacity larger than about 137 gigabytes must be an ATA-6 or later drive. Connecting such a drive to a host with an ATA-5 or earlier interface will limit the usable capacity to the maximum of the interface.

Some operating systems, including Windows XP pre-SP 1, and Windows 2000, disable 48-bit LBA by default, requiring the user to take extra steps to use the entire capacity of an ATA drive larger than about 137 gigabytes. Older operating systems, such as Windows 98, do not support 48-bit LBA at all.

July 7, 2011

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