Micro Firmware Tech Support

32 Bit Disk Access in Windows 3.1x

Filename: WIN32BDA.TXT
WWW URL:  http://www.firmware.com/support/bios/win32bda.htm
FTP URL:  ftp://ftp.firmware.com/text/win32bda.txt
Revision: 11/25/96  TLS  Micro Firmware Technical Support
Summary:  Discusses need for third-party driver to use
          32-Bit-Disk-Access in Windows 3.1x with large drives.

Windows 3.1x (3.1, 3.11, Windows for Workgroups 3.11) can use a special driver to enable it to access hard drives in "32-bit mode". This is selected with a checkbox on the Virtual Memory screen through the 386Enhanced icon in the Control Panel. It can also be turned on and off by editing a line in SYSTEM.INI.

32BitDiskAccess is not a very accurate name for this driver. Many people are confused by the name and are led to believe that this driver will allow hard drives to be accessed with a 32-bit-wide data path. This is not true - the IDE interface remains a 16-bit interface. A more accurate name might be "Protected Mode Disk Access Driver". Windows (assuming it is running in "386 Enhanced" mode) is running in what is called protected mode. This is a special mode that Intel CPUs (286 and higher) can use to allow access to memory beyond 1MB and to allow more than one program to run at the same time. DOS only uses "real mode". Normally Windows has to switch back and forth between protected mode and real mode anytime it accesses a hard drive, since Windows uses DOS services to handle drive access. The 32BitDiskAccess driver allows Windows to remain in protected mode when accessing hard drives.

The 32BitDiskAccess driver that is supplied with Windows 3.1x, WDCTRL, is limited to hard drives with 1024 cylinders or less (504MB or less). If a larger hard drive is installed and 32BitDiskAccess is enabled, Windows may lock up when started or it may return an error message such as "Insufficient memory to start Windows..." or "WDCTRL validation failed at phase XX,XX".

32BitDiskAccess should then be disabled by editing SYSTEM.INI. This is a text file in the WINDOWS directory. The DOS EDIT command can be used to edit this file. SYSTEM.INI is divided into sections with headers in square brackets. Under the [386Enh] header, you should find the entry "32BitDiskAccess=ON". To disable 32BitDiskAccess, just change the ON to OFF.

It is still possible to use 32BitDiskAccess with large drives under Windows 3.1x, using replacement drivers supplied by hard drive manufacturers.

For Western Digital drives, the replacement driver is called WDCDRV.386. The current version is 2.6. This driver is available from Micro Firmware's BBS, FTP site, and web site as a self-extracting ZIP file - WDCDRV.EXE - which contains WDCDRV.386 and WDCDRV.DOC, which explains how to install the driver. This can also be obtained from Western Digital's FTP site, BBS, and web site. This driver is also sometimes distributed as part of a collection of files in a ZIP file called WIN31.EXE. This driver can also be found on the Disk Manager diskettes that are sometimes bundled with Western Digital hard drives.

For Maxtor drives, the file WIN32BIT.EXE is available on Maxtor's FTP site at this URL: ftp://ftp.maxtor.com/pub/main/win32bit.exe This contains a version of Ontrack's 32Bit Disk Access driver, ONTRACKW.386 along with an install program and a text file, WIN32BIT.TXT, which explains installation procedure.

For Seagate drives, the file SEG32176.EXE is available on Seagate's FTP site at this URL: ftp://ftp.seagate.com/techsuppt/windows/seg32176.exe This file contains Seagate's 32BitDiskAccess driver, SEG32BIT.386 along with a text file, SEG32BIT.TXT, and an installation program.

Other drive manufacturers may have their own WIN31 32BDA drivers. Some of these may work with drives of other brands or may allow mixing of brands, or they may work only with certain brands or require that at least one drive is of a certain brand. Any questions on the use of the replacement 32BDA drivers should be directed to the drive manufacturers who supply these drivers.

Note that Windows 95 does not have the same limitations with its 32BitDiskAccess driver. WIN95 will automatically enable 32BitDiskAccess on any drive unless there is some reason it needs to limit that drive to 16-bit "DOS compatibility mode". If WIN95 has been installed over WIN3.x, it may be advisable to remove any previous 32BDA drivers that have been installed.


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