Microsoft KB Archive/51737

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Expanded Memory under Windows 3.0


The information in this article applies to:

  • Microsoft Windows versions 3.0, 3.0a


In Windows versions 3.0 and 3.0a, Windows no longer uses expanded memory for the advantage of Windows applications except in real mode.


Expanded memory management under Windows 3.0 or 3.0a is handled as follows.

Real Mode

Real mode Windows 3.0/3.0a uses expanded memory in the same manner as Windows/286 versions 2.1x.

When Windows runs in real mode, expanded memory may be provided by the following:

  • On 8088/80286 machines, an expanded memory board's driver, which is the only genuine method to obtain LIM standard expanded memory on these processors. However, of course, we recommend reconfiguring the board as extended memory if it is being used on a 286 machine and expanded memory is not absolutely required by an MS-DOS application.
  • On 386 machines, the Microsoft EMM386.SYS driver, included with the Windows 3.0/3.0a package, which converts 386 extended memory to expanded via the special capabilities of the 386 processor.

286 Protected Mode

When Windows runs in 286 protected mode, expanded memory may be provided by the following:

  • On 286 machines, an expanded memory board's driver, as above. In this case, Windows doesn't use the supplied expanded memory because Windows is running in protected mode. However, expanded memory may be used by MS-DOS applications running before, during, or after Windows.
  • On 386 machines, the Microsoft EMM386.SYS driver. Here, any extended memory converted to expanded by EMM386.SYS prior to running 286 protected mode is unavailable to Windows. Additionally, expanded memory may be allocated by an application or driver via EMM386.SYS prior to running Windows and not cause problems.

386 Enhanced Mode

In 386 enhanced mode, expanded memory may be provided by the following:

  • Windows, which provides expanded meory emulation for MS-DOS applications running under Windows in 386 enhanced mode virtual machines.
  • If expanded memory is also required outside of Windows/386 enhanced mode, it may be supplied in one of two forms depending on the requirements of the application/driver that needs expanded memory:

    • By the Microsoft EMM386.SYS driver (in a manner similar to that noted above)

      - or -
    • By the Windows/386 enhanced mode WINSTART.BAT feature. If Windows enhanced mode detects that a WINSTART.BAT batch file is present in the path when Windows is executed, the following procedure is performed:

      1. Loads the Windows/386 enhanced mode memory management, including expanded memory emulation.
      2. Runs WINSTART.BAT, allowing any programs or drivers executing therein to use the emulated expanded memory loaded in Step 1. This may include starting a network that loads network drivers in expanded memory.
      3. Loads the Windows interface.
      NOTE: WINSTART.BAT is simply a means of loading some programs in Windows that can use expanded memory. It doesn't provide expanded memory, it just allows you to run programs that want to use it.

Additional query words: 3.00 3.00a

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Technology : kbWin3xSearch kbWin300 kbWin300a

Last Reviewed: October 3, 1999
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