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Old 01-13-2006, 12:38 AM   #1 (permalink)
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Default Current HD Capacity supported by BIOS


I'm doing a research project in my PC Troubleshooting class for a little extra credit, but I'm having some problems finding some information.

We're currently studying hard drives, and the teacher said we could get some e/c if we could tell him how large of a drive most BIOS can currently support. Any reference links or information would be greatly appreciated.


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Old 01-13-2006, 12:49 AM   #2 (permalink)
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137GB is a common barrier today, which you need at least XP SP1 or Windows 2000 SP4 to overcome:
The ATA Interface Limit (128 GiB / 137 GB) Barrier

In order to avoid previous disk barriers and limitations, other than those imposed by the operating systems themselves, today's hard drives no longer rely upon discrete geometry (specific cylinder, head and sector numbers) and instead use logical block addressing and a sector number. Unfortunately, even when we move away from bit addressing in favor of head and sector numbers, we still reach the limit of our ability to address all of the bits when taken together. Let's take a look at the ATA interface. There are 28 bits used for the sector number interface with the operating system, BIOS and the hard disk. This means a hard disk can have a maximum of 2^28 or 268,435,456 sectors of 512 bytes, placing the ATA interface maximum at 128 GiB or approximately 137.4 GB.

As little as one or two years ago, no one thought there would be hard drives exceeding 137.4 GB. However, as many of you have seen, hard drive capacity surpassed this mark when Maxtor released their DiamondMax Plus 540X at 160 GB on October 29, 2001. Of course, Maxtor's release of a drive at 160 GB caught many techno-geeks off guard. How could they possibly make these huge drives work? Maxtor considered the 137 GB barrier well before releasing the drive as part of an entirely new initiative to take storage capacities into the petabyte region. To conquer the 137GB barrier, when Maxtor released their new drive, they made a new Ultra ATA/133 PCI adapter card available as part of the package. Believe it or not, for a limited period, the add-in card was "free". The adapter itself, however, was Maxtor's method of bringing these new drives to market and in the process temporarily solving the barrier problem without requiring users to purchase new computers to handle the new technology.

Significant changes have occurred to the ATA interface between the hard disk and the rest of the computer system in less than a year, and more are in the making. One entity charged with the responsibility of developing the new standards for this interface (and its changes) is Technical Committee T13. It is responsible for the coordination and development of all interface standards relating to the popular AT Attachment (ATA) storage interface utilized on most personal and mobile computers today. A few years ago a number of different proposals to expand ATA addressing from 28 bits to either 48 or 64 bits were made, and over those few years the committee examined each very closely. Either of these technology changes would permit huge drive sizes. The first to surface, however, was 48 bit addressing and delivered in the form of a hard drive at 160 GB by Maxtor. Using 48-bits like Maxtor takes drive sizes 100,000 times higher than current limits. This is most definitely a signal of what lies ahead!


Due to BIOS limitations as well as those unique to Windows®, partitioning and formatting drives larger than 137 Gigabytes without proper driver or controller support will result in data loss when storing data to the drive beyond the 137 GB Barrier.

In order for you system to recognize more than 137 GB you will need to utilize one of the following recommended solutions:

1. If you have a motherboard that has a Intel chipset (810, 810E, 810E2, 815, 815, 815E, 815EP, 815P, 820, 820E, 830M, 830MP, 830MG, 840, 845, 850, or 860) please visit Intel's web site and download the Intel Application Accelerator. Intel's Application Accelerator supports the full capacity of drives larger than 137 GB.
2. If you do not have a motherboard that has a Intel chipset then it is recommended that you purchase an Ultra ATA 133 PCI card that supports 48 bit Logical Block Addressing (LBA). You can purchase the Maxtor Ultra ATA 133 PCI Card, which supports drives that are larger than 137 GB, directly from us or your local distributor.

If you do not follow either of the above steps, and you attempt to use a drive that exceeds 137 GB and/or that relies on 48-bit Logical Block Addressing by attempting to "tweak" the system even though your ATA controller, chipset drivers and/or system BIOS do not properly support 48-bit Logical Block Addressing, data loss will occur when storing data to the drive beyond the barrier.
What will be the next barrier?

While it is true that the ATA/ATAPI-6 standard defines a method to provide a total capacity for a device of 144 petabytes, the next limit will be imposed not by the ATA devices but by many of the popular operating systems in use today. This limit will be at 2.2 terabytes (2,200 gigabytes). This barrier exists because many of today's operating systems are based on 32-bit addressing. These operating systems include many flavors of Linux, Mac OS 9.x, and Windows 95, 98, ME, NT 4, 2000, and XP (Windows XP/64-bit also has the limit because of leveraged 32-bit code).

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Old 01-13-2006, 01:01 AM   #3 (permalink)
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Thank you very much for this information, you just saved my semester 4.0!

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Old 01-13-2006, 07:36 AM   #4 (permalink)
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The 137GB barrier is related to the OS, though.
I think the 144petabytes barrier is the one.
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