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...48-bit addressing required to exceed the 137GB capacity limitation imposed by 28-bit addressing...

When the ATA disk drive interface (also known as IDE) was developed in the mid 1980's, personal computer disk drives held 20 Megabytes of data. ATA was designed with 28 bits of address, providing what seemed like a ridiculously large address space: 137,438,953,472 bytes (137 Gigabytes). Nearly 20 years later, ATA drives are available with a capacity greater than 137 Gigabytes.

To allow computer systems access all the data on drives larger than 137 Gigabytes, the T13 AT Attachment standards committee developed a new 48-bit addressing method. This method increases the address space by approximately a million fold to: 144,115,188,075,855,872 bytes (144 Petabytes).

Computer systems manufactured before development of the 48-bit address method do not support drives larger than 137GB (but can, if upgraded as described below). With some past drive capacity limitations, updating the BIOS alone solved the problem. Upgrading the BIOS doesn't hurt, but this by itself won't solve the problem unless your OS supports 48-bit addressing or you have a controller card and driver that supports 48-bit addressing.

If you've recently purchased your computer system, we advise you to check with your manufacturer to see if your system has native support for 48-bit addressing before pursuing one of the workarounds listed below. If you've already installed your drive and the capacity is listed as 137,438,953,472 bytes (137GB or 128GB), you'll need to follow one of the workarounds below to make use of the remaining space.

Note: In binary, a gigabyte is equal to 1024 megabytes, and a 137GB hard drive capacity is expressed as 128GB. So, when experiencing this capacity limitation, you may see the top capacity listed as 128GB when using a BIOS or type of software that displays the rounded binary capacity.


There are several approaches available, depending on your OS (and Chipset), when adding large disk drives to older systems:


Windows XP: Update the Operating System

Windows XP Service Pack 1 (SP1) adds 48-bit addressing support for drive capacities greater than 137GB. The boot partition can't be greater than 137GB during a fresh install (since you'll need to install Windows XP before you can apply the service pack), even if the controller BIOS supports the full capacity. You will then be able to partition the remaining space (using Disk Management) on the master drive or install and partition a slave at the full value. The boot drive must have more than one partition. However, if Windows XP Service Pack 1 (SP1) has been applied and configured on the boot drive, you can partition subsequent non-boot drives (e.g., a slave) to their full capacity. For details, see the Microsoft Knowledge Base (article #303013).

Windows 2000: Update the Operating System

Windows 2000 Service Pack 3 (SP3) adds 48-bit addressing support for drive capacities greater than 137GB. The boot partition cannot be greater than 137GB during a fresh install (since you'll need to install Windows 2000 before you can apply the service pack), even if the controller BIOS supports the full capacity. After installing the service pack to your master drive, follow the Microsoft Knowledge Base directions for making the necessary registry modifications. (Note: do not make the registry modifications before installing the service pack; it won't work.). You will then be able to partition the remaining space (using Disk Management) on the master drive or install and partition a slave at the full value. The boot drive must have more than one partition. However, if Windows 2000 Service Pack 3 (SP3) has been applied and configured on the boot drive, you can partition subsequent non-boot drives (e.g., a slave) to their full capacity. For details, see the Microsoft Knowledge Base (article #305098).

Windows 95sr2/ 98/ Me/ NT: Add in a new ATA controller card and driver with 48-bit addressing support

Some ATA adapter card manufacturers are:


Adapter manufacturer: Web site: Operating System(s):
ACARD Technology http://www.acard.com/ PC Mac
HighPoint Technologies http://www.highpoint-tech.com/ PC
Promise Technology, Inc. http://www.promise.com/
SIIG, Inc. http://www.siig.com PC Mac

Additionally, Intel has a program available for users of certain Pentium 4 chipsets that resolves the 137GB capacity limitation called the Intel Application Accelerator. This download is provided at the Intel site, along with how-to information.

Note: The list of 3rd parties above is provided for reference only and is not a recommendation of any product by Hitachi Global Storage Technologies. You should always check for compatibility and other issues with third party products, and we do not make any warranties about the use of those other products.