Microsoft KB Archive/92766

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ROM BIOS Shadowing Not an Advantage with Windows NT

Article ID: 92766

Article Last Modified on 10/31/2006


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Windows NT Workstation 4.0 Developer Edition

This article was previously published under Q92766


Some computers provide a ROM BIOS shadowing option. While this feature provides an advantage with Microsoft MS-DOS, it is not an advantage with Microsoft Windows NT.


ROM BIOS shadowing is the process of copying the BIOS from ROM into RAM and using either hardware or 386 enhanced mode to remap the RAM into the normal address space of the BIOS. Because reading RAM is much faster than reading ROM, BIOS-intensive operations are substantially faster. For example, MS- DOS uses the BIOS to write to the screen; therefore, with ROM BIOS shadowing, directory listings run more quickly.

Windows NT does not use the BIOS (except during startup); therefore, no performance is gained by shadowing. If ROM BIOS shadowing is not used, more RAM is available. With Windows NT, there is an advantage to disabling the ROM BIOS shadowing option.

This applies to other BIOS shadowing schemes as well. Typically the CMOS settings allow the system to shadow any BIOS. This includes the following:

System BIOS
Video BIOS
Other adapters ROM BIOS (in a given select range)

Additional query words: prodnt win32

Keywords: kbenv KB92766