Microsoft KB Archive/83363

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Unlocking Large-Model Extra Data Segments

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Q83363

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The information in this article applies to:


 * Microsoft Windows Software Development Kit (SDK) versions 3.0, 3.1

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SUMMARY
An application that is compiled using the large memory model can have multiple code segments and multiple data segments.

Under Windows 3.0, all the data segments except for the first one (the so called &quot;extra&quot; data segments) are loaded into memory segments that are fixed and page locked. Fixed and page locked segments interfere with effective memory management. They reduce the amount of free memory addressed below 1 megabyte (MB) in the linear address space, and in some cases, cause out-of-memory errors as additional applications are run.

Under Windows 3.1, extra data segments are loaded into movable memory and the above difficulties with fixed and page locked segments do not apply.

A large model application can change the attributes of its extra data segments by calling the GlobalPageUnlock and GlobalUnfix functions. However, to do this effectively, the application must be able to enumerate the selectors for its extra data segments.

Largeapp.exe is a file in the Microsoft Software Library that demonstrates using the GlobalPageUnlock and GlobalUnfix functions to change the attributes of an application's extra data segments. Largeapp.exe contains the source code to two applications: Largeapp.exe, which is a large-model application for the Windows environment, and SYMSEG, which is an MS-DOS (non-Windows) application.

SYMSEG is a utility that reads a symbol file produced by the Microsoft Linker, and creates a table of the data segments in an application. LARGEAPP uses the information from this table to enumerate its own data segments.

MORE INFORMATION
The following files are available for download from the Microsoft Download Center:

Largeapp.exe

For additional information about how to download Microsoft Support files, click the article number below to view the article in the Microsoft Knowledge Base:

"Q119591 How to Obtain Microsoft Support Files from Online Services" Microsoft used the most current virus detection software available on the date of posting to scan this file for viruses. Once posted, the file is housed on secure servers that prevent any unauthorized changes to the file.

LARGEAPP determines the version of Windows under which it is running. The segment attributes must be changed only if the application is running under Windows 3.0.

Additional query words: softlib LARGEAPP.ZIP

Keywords : kbfile kbsample kb16bitonly kbOSWin310 kbOSWin300

Issue type :

Technology : kbAudDeveloper kbWin3xSearch kbSDKSearch kbWinSDKSearch kbWinSDK300 kbWinSDK310