TITLE
    DOS Compatibility Card: Less RAM Than Set In PC Setup (10/95)
Article ID:
Created:
Modified: 		18386
8/15/95
10/9/95
TOPIC


    I have 40 MB of RAM in my Macintosh, and I have selected 16 MB for my DOS Compatibility Card in the PC Setup control panel. However, my DOS Compatibility Card will only access 8 MB of RAM. I thought I could access half of the RAM. Why does this happen?

DISCUSSION


    Yes, it is true that you can allocate half of the total physical RAM to the DOS Compatibility Card using shared memory. However, the only choices are the ones in the menu of the PC Setup control which are: 2, 4, 8, 16, 32. There are choices for 1 and 64 but none of these are ever available, even with a full load of RAM. Since you have 40 MB RAM, the closest number to 20 (half of 40) is 16. Therefore, you can, at most, share 16 MB RAM with the DOS Compatibility Card.

    You cannot share virtual memory (VM) to the DOS Compatibility Card. If the system only has 16 MB RAM and you set VM to 32 MB, you can still only share a maximum of 8 MB RAM.

    There are two situations that must be kept in mind when sharing RAM between a Macintosh and DOS Compatibility Card. Both can affect the DOS Compatibility Card, they are as follows:

    When changing the RAM allocation in the PC Setup control panel, you must restart the Macintosh before the RAM change will take effect.

    During startup, if you have several extensions or control panels load before PC Setup, a reduced amount of RAM will be available for the DOS Compatibility Card. For example, having a large RAM Disk mount at startup may allocate enough memory before PC Setup loads forcing it to reduce its memory allocation below the control panel setting. If this happens, you must evaluate whether all of your extensions and/or control panels are necessary, and turn those off which are not.


    This article was published in the "Information Alley":
    Volume II, Issue 12, Page 13


    Article Change History:
    09 Oct 1995 - Added Info Alley information; updated article.

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Document Information
Product Area: Computers
Category: DOS Compatible
Sub Category: DOS Compatibility Cards
Keywords: kwindows,kalley

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