How to Increase the DOS Conventional Memory in a Virtual Machine

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Article ID: 825463 - View products that this article applies to.
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SUMMARY

This article describes how to increase the MS-DOS conventional memory in a virtual machine.

MS-DOS-based programs use some conventional memory to run, even when you run them in Windows. The conventional memory area is the 0K-640K section of memory. MS-DOS and typical program software use this area of memory.

If you try to run an MS-DOS-based program that uses more conventional memory than your computer currently has available, the program may not run correctly or at all. You may also receive an error message that says that there is not sufficient memory to run the program. When this behavior occurs, you must reconfigure your computer so that more conventional memory is available. To do so, edit the Config.sys file.

Note Back up the Config.sys file before you make any changes.

To edit the Config.sys file, use any of the following methods:
  • Use a text editor such as Notepad to edit the Config.sys file.
  • In Microsoft Windows 98 or Microsoft Windows Millennium Edition, use the sysedit command. To do so, click Start, click Run, type sysedit in the Open box, click OK, and then click C:\Config.sys on the Windows menu.
  • In a DOS window, type:
    edit C:\CONFIG.SYS
To edit the Config.sys file to make more conventional memory available, use any of the following methods:
  • Add the following lines at the beginning of the text in the CONFIG.SYS file:
    DEVICE=C:\WINDOWS\HIMEM.SYS
    DEVICE=C:\WINDOWS\EMM386.EXE RAM
    Note The RAM switch at the end of the second line permits Expanded Memory Specification (EMS) memory.
  • You can set the area of random access memory (RAM) that you want EMS to use. If you do this, you must use an area that nothing else uses. For example, to use a memory address that is reserved for monochrome displays (that are no longer used), use the following lines instead:
    DEVICE=C:\WINDOWS\HIMEM.SYS
    DEVICE=C:\WINDOWS\EMM386.EXE RAM I-B000-B7FF
  • If your program requires a particular amount of memory, you can set the EMS size to a fixed amount. If you do not set the EMS size, the program may use more than you want it to use. Typically, it is best practice not to set a fixed size. For example, if a program must use 4 MB of EMS, use the following lines instead:
    DEVICE=C:\WINDOWS\HIMEM.SYS
    DEVICE=C:\WINDOWS\EMM386.EXE 4096
After you make the changes, save the file, and then restart the virtual machine.

MORE INFORMATION

For additional information about how to increase conventional memory for MS-DOS-Based programs, click the following article numbers to view the articles in the Microsoft Knowledge Base:
134399 How to Increase Conventional Memory for MS-DOS-Based Programs
37242 A General Tutorial on the Various Forms of Memory
77083 Optimizing Your Use of Upper Memory Blocks
87165 Command-Line Switches for MSCDEX.EXE
151718 Managing Memory in MS-DOS Mode

Properties

Article ID: 825463 - Last Review: September 10, 2011 - Revision: 3.0
APPLIES TO
  • Microsoft Virtual PC for Mac Version 6.1
Keywords: 
kbinfo KB825463

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