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Microsoft KB Archive/101750

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Knowledge Base

PC Ext: Overlay Files and How They Work

Article ID: 101750

Article Last Modified on 10/30/2006


  • Microsoft Mail for PC Networks 3.2

This article was previously published under Q101750


The External Mail program (EXTERNAL.EXE) included with version 3.2 of Microsoft Mail for PC Networks introduces overlay files to control different forms of communication. These files are loaded into extended memory and introduce the need for EXTERNAL.EXE to be stored on the local computer.

There are three overlay files, which provide the following functions:

  • The AYSNC.OVL file controls asynchronous communication.
  • The X25EICON.OVL file controls communication with the Eicon X.25 card.
  • The X25ATLAN.OVL file controls communication with the Atlantis X.25 card.

The External Mail program must load one of these overlay files because these files contain shared code for the Mailer and Dispatch processes to distribute messages on the network.

By loading this part of the process into extended memory, more postoffices can be controlled by the External Mail program, thus getting around the memory constraints of version 3.0 of the External Mail program.

Additional query words: 3.20

Keywords: KB101750