BIOS Translation

BIOS Translation

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BIOS translation is one of the most important techniques used to overcome the 504 MB disk size barrier that resulted from the combination of BIOS and IDE/ATA hard disk restrictions. Since this is often a confusing subject, we have provided additional detail with respect to the various types of BIOS translations that are in use in personal computers. A BIOS that supports the extended CHS and/or LBA modes is referred to as an enhanced BIOS.

The table below provides a comparison of the three translation modes, showing a summary of each beginning at the operating system level, through the BIOS to the hard disk controller and then to the physical drive:

Interface

Standard CHS

Extended CHS (ECHS) / Large

Logical Block Addressing

Physical Drive Platters to Integrated Disk Controller

Physical Geometry

Physical Geometry

Physical Geometry

Integrated Disk Controller to BIOS

Logical Geometry

Logical Geometry

Logical Block Address

BIOS to Operating System and Applications (through Int 13h)

Logical Geometry

Translated Geometry

Translated Geometry

Notice that in all cases the physical geometry is hidden within the hard disk itself. In the case of LBA, the logical geometry is presented to the BIOS only to have it translated for use by the operating system. Communication between the BIOS and the hard disk controller occurs through the use of the logical block address.

When Installing Windows® 2000 or Windows® XP – Setup does not check for INT-13 extensions before creating a system partition.

When you install Windows® 2000 or Windows® XP, setup allows you to delete, create, and format the system/boot partition. Neither Windows® 2000 or Windows® XP imposes any restriction on the size of the system/boot partition because it can format the partition using the FAT file system (up to 2 gigabytes, or GB), the FAT32 file system (up to 32 GB) or the NTFS file system (up to 2 terabytes) before copying its setup files.

The system partition is defined as the partition containing the files needed for the initial system startup. For Windows® 2000 and Windows® XP, these are the Ntdetect.com, NTLDR, Boot.ini, and under certain circumstances Ntbootdd.sys files.

Both Windows® 2000 and Windows® XP support large system partitions because they have the ability to use BIOS INT-13 extensions to boot the operating system on partitions with more than 1,024 cylinders, or 7.8 GB in size. After Windows® 2000 and Windows® XP setup copies files, it restarts the computer to continue with GUI portion of their setup mode.

Although the foregoing was first discovered in SCSI based systems, and thus the Microsoft Knowledge Base Article referenced below addresses systems with a SCSI interface, the information is still relevant for IDE/ATA based systems.

To read more about this issue, visit the Microsoft Knowledge Base. You can click here and review a brief popup of this article or visit the Microsoft Knowledge Base and Review Article Q240672.

Notice: Windows® 95, Windows® 98, Windows® NT, Windows® 2000, Windows® XP and Microsoft® Office are registered trademarks or trademarks of the Microsoft Corporation.

All other trademarks are the property of their respective owners.

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