Logical Block Addressing (LBA) Defined

This article was previously published under Q122052
Retired KB Content Disclaimer
This article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
Logical Block Addressing (LBA) is a method of accessing hard disk drives.This allows IDE disks larger than 504 megabytes (1024 cylinders) in sizeto be fully partitioned using the MS-DOS fdisk command. Prior to thistechnology, ROM BIOS limitations prevented the fdisk command from using anentire hard disk that was larger than 504 megabytes (MB) in size, exceptby using other controller ROM routines that effectively translate the harddisk's native geometry.
LBA is a run-time function of the system BIOS. The BIOS uses LBA for thefollowing commands: read (with and without retries), read verify, readlong, write (with and without retries), write verify, write long, readmultiple, write multiple, read DMA, write DMA, seek, and format track.

As with non-LBA systems, information about the hard disk's true geometry isstored in the system CMOS. When reporting information about the hard diskto MS-DOS, however, a system employing LBA essentially depicts a hard diskwith fewer than 1024 cylinders and the LBA BIOS performs a translation fromthe MS-DOS track, head, and sector to logical block numbers used by thedrive, allowing the entire disk to be used without special drivers or third-party disk utilities.

The LBA standard specifies the following two types of drive parametertables:
  • Automatic (recommended for Novell NetWare and Unix).
  • Translation (recommended for MS-DOS, Windows, OS/2 2.x, and Windows NT).
The following sections provide information about the use of LBA withvarious BIOS chip sets, including the specific versions of these BIOS chipsets that support LBA.

American Megatrends Inc.

American Megatrends, Inc. has confirmed that versions of its BIOS dated4-25-94 and later are compatible with LBA. For more information, contactAmerican Megatrends.


Micro Firmware, the sole provider of BIOS upgrades for Phoenix BIOS chipsets, has confirmed that BIOS versions 4.03 and later are compatible withLBA. However, various computer and system board manufacturers may be usingspecific revisions of the version 4.03 BIOS that do not support LBA. Inthese cases, the hardware manufacturer should be contacted for anappropriate BIOS upgrade. For more information, contact Micro Firmware.

This article refers to products manufactured by vendors independent ofMicrosoft; we make no warranty, implied or otherwise, regarding theseproducts' performance or reliability.
ata eide translation gb gigabyte ami

Article ID: 122052 - Last Review: 12/17/2000 15:50:00 - Revision: 1.0

  • Microsoft MS-DOS 6.0 Standard Edition
  • Microsoft MS-DOS 6.2 Standard Edition
  • Microsoft MS-DOS 6.21 Standard Edition
  • Microsoft MS-DOS 6.22 Standard Edition
  • Microsoft Windows 95
  • KB122052