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Q122052: Logical Block Addressing (LBA) Defined

Article: Q122052
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:6.0,6.2,6.21,6.22; WINDOWS:95
Operating System(s): 
Keyword(s): 
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 6.0, 6.2, 6.21, 6.22 
- Microsoft Windows 95 
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SUMMARY
=======

Logical Block Addressing (LBA) is a method of accessing hard disk drives. This
allows IDE disks larger than 504 megabytes (1024 cylinders) in size to be fully
partitioned using the MS-DOS fdisk command. Prior to this technology, ROM BIOS
limitations prevented the fdisk command from using an entire hard disk that was
larger than 504 megabytes (MB) in size, except by using other controller ROM
routines that effectively translate the hard disk's native geometry.

MORE INFORMATION
================

LBA is a run-time function of the system BIOS. The BIOS uses LBA for the
following commands: read (with and without retries), read verify, read long,
write (with and without retries), write verify, write long, read multiple, write
multiple, read DMA, write DMA, seek, and format track.

As with non-LBA systems, information about the hard disk's true geometry is
stored in the system CMOS. When reporting information about the hard disk to
MS-DOS, however, a system employing LBA essentially depicts a hard disk with
fewer than 1024 cylinders and the LBA BIOS performs a translation from the
MS-DOS track, head, and sector to logical block numbers used by the drive,
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 parameter tables:

- 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 with various BIOS
chip sets, including the specific versions of these BIOS chip sets that support
LBA.

American Megatrends Inc.
------------------------

American Megatrends, Inc. has confirmed that versions of its BIOS dated 4-25-94
and later are compatible with LBA. For more information, contact American
Megatrends.

Phoenix
-------

Micro Firmware, the sole provider of BIOS upgrades for Phoenix BIOS chip sets,
has confirmed that BIOS versions 4.03 and later are compatible with LBA.
However, various computer and system board manufacturers may be using specific
revisions of the version 4.03 BIOS that do not support LBA. In these cases, the
hardware manufacturer should be contacted for an appropriate BIOS upgrade. For
more information, contact Micro Firmware.


This article refers to products manufactured by vendors independent of Microsoft;
we make no warranty, implied or otherwise, regarding these products' performance
or reliability.

Additional query words: ata eide translation gb gigabyte ami

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Keywords          :  
Technology        : kbWin95search kbZNotKeyword3 kbMSDOSSearch kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600
Version           : MS-DOS:6.0,6.2,6.21,6.22; WINDOWS:95

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