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The BIOS limitation or BIOS capacity barrier is the computer’s inability to recognize hard drive capacities larger than allowed by the hard-coded programming contained in your system BIOS. For example, your system BIOS might only be capable of understanding a hard drive capacity of up to 32 GB. If you then attempt to install and auto-detect a 40 GB hard drive, the system will freeze because the BIOS is not capable of understanding the capacity reported by the hard drive. In short, that particular BIOS cannot count past 32 GB.

Seven Major BIOS Limitations:

• Systems with BIOS dated prior to July 1994 (504 MB Limitation).
  Typically these BIOS will have a 504 megabyte (1,024 cylinders) limitation. Prior to this date, most manufacturers’ BIOS did not provide the Logical Block Address (LBA) feature needed for proper translation. Some BIOS had LBA mode in the setup, but the feature did not work properly.
• Systems with BIOS dated after July of 1994 (2.048 GB Limitation).
  Typically, these BIOS provide support for hard drives with capacities larger than 504 megabytes. However, depending on the manufacturer’s release date and version number, different limitations may be encountered. The major limitation that surfaces is the 4,093-4,096 cylinder limitation. This barrier is derived from the fact that some BIOS manufacturers implemented Logical Block Addressing (LBA) translation in their BIOS with a 4,093 – 4,096 cylinder limitation. System hangs would occur when the cylinder limitation threshold is exceeded. A system hang is defined when the operating system hangs during initial loading, either from floppy diskette or existing hard drives. If these symptoms of system hang occur or there are questions whether the system BIOS will support the drive, contact the system or motherboard manufacturer for assistance.
• 4.2 GB Limitation.
  The maximum parameters at the 4.2 GB barrier are 8,190 cylinders, 16 heads and 63 sectors for a capacity of 4.2 GB. A system hang is defined when the operating system stops responding during initial loading, either from floppy diskette or existing hard drives. This can be caused by the BIOS reporting the number of heads to the operating system as 256 (100h). The register size DOS/Windows 95 uses for the head count has a capacity of two hex digits. This is equivalent to decimal values 255. If these symptoms of system hang occur or there are questions whether the system BIOS will support the drive, contact the system or motherboard manufacturer for assistance.
• 8.4 GB limitation.
  The maximum parameters at the 8.4 GB barrier are 16,383 cylinders, 16 heads and 63 sectors for a capacity of 8.455 GB. To go beyond this boundary, a new extended INT 13 function is needed from the BIOS as a support feature for the drives. The BIOS listed below are all “CORE” BIOS that will support drives larger than 8.4 GB. Even though a BIOS is dated correctly or is the current version, it may not be able to support extended interrupt 13 because of modification done to the “CORE” of the BIOS from the motherboard manufacturer.
• 32 GB limitation.
  This condition is caused by the Award BIOS inability to address hard drives greater than 32GB. Award has been made aware of this issue and has fixed their “core” BIOS as of 6/99. They are passing this information along to the motherboard manufacturers’ that use their BIOS. Updates for the BIOS should be available soon from individual motherboard manufacturers’ to correct this problem.
• 64 GB Limitation
  There is no 64GB BIOS Capacity Barrier. If you use FDISK to format a drive that is larger than 64 GB, FDISK will report the incorrect disk size.
• 137 GB Limitation
  Some system BIOSes are limited to 137 GB because they can only support 28 bit Logical Block Addressing (LBA).

Procedure on how to overcome the BIOS capacity limitation:

• Check with the system or motherboard manufacturer for any BIOS upgrades for the system. If there are no BIOS updates from the manufacturer you can visit www.esupport.com for a BIOS update.
• (Recommended) Purchase a PCI ATA controller card that will support the capacity of the drive. The two benefits of ATA controller cards are:
1. the ability to support large capacity drives
2. the ability to support the faster transfer rates of the drive.